Eh, probably not. More likely, they are AT-type keyboard connectors (5-pin round DIN plugs, about 1/2" in diameter). It was the mice that used the 9-pin D-sub serial connectors you’re referring to for that generation of machines.
Crap, you’re right. I forgot about those.
I’m pretty sure that it dates back to at least Windows 98 Second Edition, which is about as far back as I can remember using it. It’s certainly there in Windows 2000. However, since it’s considered part of Windows’ “Accessibility Options”, it may be an optional item at the point of OS installation, although ISTM that on XP systems it’s installed by default.
I use it all the time; for probably 80% or more of my Web-browsing, I don’t have a keyboard immediately to hand, so the On-Screen Keyboard (“osk.exe”) is always loaded and ready to go. With judicious use of macros and jump-pages, it’s amazing what you can do with just the mouse (if you know in advance that that’s how you’re going to be working!).
An example: I’m lying down, watching a DVD on the PC, and the lights are out. The mouse is within reach of my right hand, but I don’t particularly want the keyboard on my lap – I can’t read the keys anyway, and I’m at best a 90%-accurate touch-typist. If I want to pause the movie and look something up (why are you all looking at me like that – doesn’t everyone do this?), I can minimize the DVD, and type whatever I need in Google or Wikipedia using OSK, and a few seconds (or hours…) I’m ready to go back to the movie.
For writing a document of more than a couple of dozen characters (such as this post), however, it’s obviously much faster to use the keyboard.
Heh, reminds me of when my sister had digital cable and writing emails was done via the remote control 
Ahh - the digital equivalent of making a ransom note from cut up newspaper headlines.
Si
The same violent storm hit me last night, probably 30 minutes before you, but I was merrily typing and mousing away all during and after the heavy downpour with no damage. I must have all the luck.
I thought that very thing while trying to post!
You got it!
Should it install from Accessibility Options in XP Pro?
You can buy adapters to convert those to standard PS/2, although that won’t do you any good with your current situation. Just an FYI for future reference.
Man, I’ve got the opposite problem. Too many USB things and too few USB ports. Gotta get me another USB2 card…
They have USB hubs/splitters you can get much cheaper and install much easier than a card. I have 7 things plugged into one USB port on my laptop using the hub. That way, I can have all my peripherals able to be plugged in with one USB plug when my laptop is at my desk… it is easier to plug into and out of “homebase” that way.
Amateur. You should try rubbing a paper clip in your hair to build up just the right amount of static electricity and then tapping lightly on the internal processors in just the right place. 
edited because I didn’t bother to preview.