Nicky,

I went two years ago and loved every minute of it. I stayed up North though, and never made it down to my own birth city (HCMC). I'll do that next time.

I really liked the Lonely Planet Vietnam guide and I got a lot of information from vietnamadventures.com

The only ideas off the top of my head are..

unless you are going to be with family..stay away during Tet.

and..

brush up on your haggling skills

Feel free to pop me an email if you think there's something else I might be able to help you with.