I went to Vietnam in early 03, I believe tourism has developed more since then, but even so, was still very easy to get around. I’ll give you some broad hints, if you’d like more information, feel free to ask or email me.
My friend and I organised everything ourselves, so no tour guides etc other than a 2 day trip down to Can Tho which was around US$20 IIRC, for all travel and accommodation etc.
We spent 5 days in Saigon, 2 down the Mekong Delta, 3 or so in Hoi An (fly to Danang, but don’t stop there, take taxi 45min south) could have spent longer, 3 days Hue (more than enough!), 5 in Hanoi - weather prevented us doing Highlands or Halong Bay, but apparently both well worth it.
Travel internally takes a long time - we had a month there and took some internal flights on Vietnam Air to save time - don’t bother buying these tickets until you get to Vietnam, much cheaper to buy from a local office, and absolutely no problems, just walk into any office (quite common on main streets). Lots of foreign pilots (ours seemed to all be British). Don’t eat the meal, it was the only time my friend got sick our entire time there.
Food is really cheap, and we ate well, most of the hotels put on some sort of breakfast, but if you want something very cheap (and can’t face soup first thing in the morning like me!) there are bakeries on a lot of the streets. Fantastic bread being sold on the streets as well, like 25c a roll etc. Careful as some meat products are placed in things that look like donuts, just be aware!
We tried to avoid standard backpacker areas in the main cities, finding it was a little more peaceful and (more importantly) less likely to be hassled on the street. We paid around US$20 a room or less per night, that’s middle of the road accommodation, includes TV, sometimes cable, airconditioning etc. Can get as low as around US$4-8 a night (but very basic), or much more pricy if you want lots of atmosphere or US style service.
So we stayed at:
Four Roses hotel Saigon - beautiful, basic English/French spoken, about 30-40 min walk from main centre of town
Cao Dai Hotel Hoi An - great colonial style hotel about 5 min walk from town. Lovely staff, arranged minibus for us from Hoi An to Hue, $4 each, takes 6 hours, not a nice drive! But all roads like that basically.
Can’t remember where we stayed in Hue or Hanoi (other than in Old Quarter), but both were pretty average, lots of choice so shop around.
I emailed hotels directly after finding details on the Internet, definately the cheapest way to book, going through a travel agent for both hotels and flights doubled the cost.
I never felt threatened at all, basically at 5’4" I was taller than most of the people there and people were also in almost every case very friendly. It was never very quiet, but we were sensible and didn’t walk around late or anything.
Know roughly how much things cost, people will see that you are a tourist and automatically quote a higher price - feel free to barter if you think they are having you on, but also remember that a $2 difference for you is nothing, but is a huge amount for a country where the average wage is $250 or less.
Learn a couple of phrases in Vietnamese - thank you, please, hello child/old man/old woman etc - worth it for both the ‘grease’ on the wheels, plus the pure delight on people’s faces when you do.
Get used to being looked at, and don’t take it personally.
The traffic is crazy. There are no road rules, and no chance for the traffic to stop to let you cross. You have to be zen-like, just start walking across the road, at a constant pace, and trust that they will miss you. Don’t try and dodge, you’ll only get hit!
I absoutely loved my time there, hope you can tell, and I think I will shut up now! But feel free to ask more if there is something specific you want to know.