A 60 gig drive will work well for a boot drive, but don't get anything smaller. Even if you manage all your programs and downloads diligently, you will quickly find that you will be using about 30 gig or so. A 60gig drive will allow to install a few things that work hand in hand with your OS, like a browser, your antivirus software, a few odds and ends like that. A 120 gig SSD for an OS drive is really preferred, you can install a few other things like the game you are playing the most right now.
And yes, using an SSD as a boot drive speeds up everything, even if you do like me and use a secondary SATA II mechanical drive to store all your games and programs. Most of these load into memory and only go back to the drive occasionally anyway, so once they get started and loaded, if you have 8 gig or so of memory, trips back to the drive to get data can be much fewer.