I have been holding off Vista for ages but after upgrading to Core i7 and 6GB of RAM it was necessary.
I am running Vista x64 business and after 1 weekend of messing around and reinstalling twice i have got it working just great. Give it a week to 'settle in' as there is a lot of hard drive thrashing due to file indexing and superfetch.
As far as support goes:
All my drivers work without any problems. nVidia who was notorious for making dog **** Vista 64 drivers installed and work without blinking an eyelid.
Sound Blaster Xtreme Gamer drivers work without problems.
Motherboard drivers was downloaded from Intel for my X58. I did have problems with my DVD drive after installing Service Pack 1, but installing the Intel Matrix Storage Manager fixed these issues.
Just make sure you hunt for 64 bit versions of your software such as any DVD image mounting software, disk de-fraggers and most importantly; anti virus software.
There are two Program Files entries in C:, Program Files x86 and Program files x64. Non native 64 bit software goes in the former and native goes in the latter.
All my Steam games work fine including Killing Floor and RO. As for the question of copying the folder, run your Steam backup utility and backup RO. You can restore this after you have installed Vista and it will work fine. I did this for all my games when i was running XP 32 and they all restored just fine.
I did try XP Pro x64 but after installing my chipset drivers i had terrible mouse problems so i went back to Vista, but the option is there for you decide Vista is not for you. Remeber that you can always download a 'trial' for both.
If you do go for Vista make sure you download
Service Pack 2.