My vote goes for the phone call. Quick, brief, not threatening, in my opinion. Seems more like an impulse than a planned out thing too, definitely less stalker like.
And I totally agree - whatever you decide to do, DO SOMETHING!!!
I can’t believe no one has suggested this.
Can you find her e-mail address?
All the charm of a short note and easier to repsond to, with none of the potential discomfort of a phone call.
I recently ran across an old college girlfriend on the Net, dropped her an e-mail. Apparently she thought about it overnight and decided I wasn’t trying to stalk her. We’ve had several nice exchanges since then.
Dude, it has been six days. Now is the time to call your babies!
And don’t forget, you’re money, baby!
I agree with your original of sending a little note. Keep it casual, as maybe she doesn’t know yet how involved she is with this guy. If it’s getting serious, then you don’t want to come across as hitting on her. Just a little note saying that you’d like to keep in touch. That leaves the ball in her court, with no pressure. And if things change with her, she’ll still have your phone number and e-mail address.
DEFINITELY get in touch with her–as has been said, you have nothing to lose and everything to gain. I would be flattered if I ran into a guy from HS and he remembered me and was interested.
A phone call is OK as long as you keep it casual–“It was so nice running into you like that. I’d like to get together and catch up, how about coffee or lunch?” If you don’t feel up to a call, a note or card would be good–the postcard does have the problem of being readable by any- and everyone. Do give her multiple ways of reaching you–phone, including work if she can call you there, and email. Definitely mention that you got her number or address from the phone book.
Good luck!
Call her.
Speaking for myself, a note is a cute idea, and I would enjoy getting one. But, I would never respond - not necessarily because I was not interested - just because I’m too busy and personal things slip my mind easily. By the time I would get around to responding, a week or two would have passed, then I would be too embarrassed to respond because so much time had passed.
Like the others said, keep it light, lunch or coffee to “catch up and talk about the good old days” - I would love a call like that.
Hmmm, just what I was afraid of:
[li]phone call = 10 votes[/li][li]postcard or letter = 8 votes[/li][li]undecided = 2 votes[/li][li]misc = 3 votes[/li]
::::sigh:::: Looks like majority rule is to call, which scares the poop outta me. What if John Doe answers the phone?
I like the email idea. She told me she works as computer op. at the hospital. I’m sure she has email. I think I will try Classmates.com and see if she’s registered. If not, I guess I gotta do the snail mail thing with a fun card and short note. Thanks people 
So, MSK, whatdja end up doing?
Details. We want some details.
I waited too long. I had other more important things to do, like get a newe job (which I did) and take care of other priorites. Damn responsibility, damn it to hell! lol Never gonna get any dates now. I will be working my ass off.
(Charlton Heston voice: at end of Planet of the Apes)
DAMN typos! Damn them all to helllllll!
It’s not too late, so stop wimping out.
Look, you’ve been a busy guy… you just got a new job… you’re a go-getter. Trust me, she’ll understand. What better excuse is there? I mean, more bucks for her to suck out of you as she turns you into nothing more than a head-nodding, walking ATM, the good-for-noth… uh oh… sorry I got a little carried away with my own problems there. I’m sure your friend is a lovely girl.
Seriously, though. She still remembers you, and the situation is NOT unsalvageable… I KNOW the other Dopers would agree with me.
Make a deal with yourself right now. Here are the terms:
Stop beating yourself up for not having contacted her(carrot) but resolve to do it now (stick).
That being said, send that email. Or make that call. Or mail that postcard.
Go ahead, do it now.
Call her.
Just be friendly. Tell her she popped up in your thoughts again today (possibly mention something that reminded you of her). Act casual and just suggest you don’t think you should leave it so long before catching up again. Suggest a coffee - non-threatening, casual and friendly. The trick (if you want to call it that) is to appear a little indifferent.
Ignore the second paragraph perhaps but give her a call!!! The only thing you’ve got to lose is a reason to gripe about what could have been.
Carpe diem (at worst you can carpe cerevisi later)
MSK:
You know dpr is right.
You know I’m right.
Call her. It really is no big deal.
(Hey dpr, what is it with you Australian guys and the humorless 3-consonant handles… namely dpr and pLt? Just a coincidence?)
And if Mr Doe answers, then at least you know there IS one and you can save your pride in the knowledge that she rejected you for a good 3d party reason and not because she thinks you’re icky. With an unreturned letter you would never have any clue as to what her response was.
flower - you look like a stalker, what if her “other” sees it. What if she’s not interested, then she’s stuck with a flower, and the dilema of how to bruch you off. Which will eventually lead to a phone call, she decides when to call you. Meanwhile, you’re stuck with the question, did she get it?, did she like it? etc, etc, etc…
note - see flower.
Call her. Ask her out, cut out the middleman. Then you will immediatelly have your answer and not have to worry about what she thinks, because you will know.
That’s how Ponch would handle it. But then again, what do I know.
MSK:
It’s not too late.
It is almost never too late.
Call her, already.
Email is probably the easiest way to do it. However, it’s a good idea only if you know how to write decently.
BTW if you need a Cyrano here I’ve pulled this off successfully before. 
Second vote would be phone call. But another problem with that is the possibility no one is at home - then you’re stuck leaving a message, which is always awkward. Nobody alive can leave a good message.
Lastly - A flower, even one, is too much. Flowers are for when you’ve fucked up, not before you get started.
Flowers are for ANYTIME. Just pick the right ones.
Phone calls say you are too lazy to come in person.
Email says you are too lazy or uninterested to call.
Go see her, ask her, ‘what time would you like to have dinner tonight, 530pm or 630pm?’
Also, Cyrano is on the net. Have him write you a love letter:
http://www.nando.net/toys/cyrano.html
MSK,
If it’s been YEARS since high school and she was glad to see you, how is a week too late??? DON’T WIMP! You know you want to. DO IT!!! And a big WOOHOO on the job! Can we get details???