I would not recommend installing Vista on any drive smaller than 60GB. The reason I say this, is even if your base install fits, as you use the machine, the WinSxS folder gets much larger as you install/uninstall programs. On my current machine the WinSxS folder is nearly 20GB alone, not counting any swap file, programs or Windows on that drive.

After a few months of running on a 30Gb drive, you will start to see that no matter what you do to clean up temp files, you will be constantly plagued by out of space issues.

Oh, and Audience... it is SSD, not SDD