**Make sure you get the bolt in kit for the S1283.**
You won't "need" a 64bit OS, it's just that on 32 bit you are limited to only 3.5GB RAM.
If your games, printers,etc have Vista x64 drivers and will run on Vista x64 then get Vista x64, else get Vista or XP.
LCD? Any thing less than a 22" is probably a waste with that 4870 X2.