that would depend whether or not you count games as programs I have a dedicated drive just for games and it has about 160gb on it, my regular software + windows is about 16gb
Not many actually, at home I have Office '07, visio, an FTP client, iTunes (shudder), and some CD/DVD burning software and that's pretty much it. This is on my main computer, takes about 10GB I'd estimate. That excludes Vista