It is better on balance to get one 80gb ssd instead of two 40gb ssd's in raid-0. It is cheaper, and will perform better.
Agree. Stay away from RAID for SSD, unless you really know what your are doing. TRIM is NOT supported in RAID, unless the drive in NOT part of a RAID array. Windows 7 is also required for TRIM.
My system is setup that way, see below. Many other threads about this topic: SSD vs. Raid vs TRIM.
Back to the Original Post: 32GB maybe big enough. You'll have to check the size of your OS. Hard to do if other things are on the drive, too (i.e. Document, Music, etc.).
However, My OS drive, I think, is 46GB with Win7 Home, Office 2007, Quicken, Norton 360, and a few other downloads, no games. I'll check and post my size later.
I have "My Documents, Music, Pictures, Video, and Downloads" on another drive, with yet another for backups.
To be sure, go with at least 60GB, 80GB would be better.