One tool you will absolutely have to have is ADMT 2.0 that will let you migrate your accounts if you don't do an inplace upgrade.
http://www.microsoft.com/downloads/details.aspx?FamilyID=e92cf6a0-76f0-4e25-8de0-19544062a6e6&displaylang=en
that is a link to a migration document from Microsoft. There are a lot of docs on the MS site that are actually accurate and good.
As for experience conducting this migration, I've had a few glitches here and there on the ones I've done, thus I prefer to conduct a parallel upgrade if the hardware is available. The process for the inplace upgrade does involve more downtime but it works as well. Again all of this is refernced. you can find a great deal of this at www.microsoft.com/technet
You might also consider either getting a few folks MCSE/MCSA certified or pull in a Engineer from your prefered VAR. A really good VAR for this kinda work with a national presence is Alternative Technologies. Your local VAR can arrange to have them send an engineer for you because they don't take direct customer work.