A quick scan with Spacemonger confirmed that 90% of the disk was filled with games. I decided to be moderately ruthless and un-install any game I haven't played in over a year.
Some folk have a strong sentimental attachment to their save games as this terrific piece by Lara Crigger in Gamers with Jobs testifies. There was time when I felt the same way. I was so proud to have completed Doom / Descent / Half Life that I religiously copied my save games from one PC to the next each time I upgraded. Now however I seem to have outgrown that. There are too many games and just too little time. The truth is that even when I do go back to an older game I generally start over from the beginning. Unless I seriously think I am going to use them again the save games are going too.
By the way I am using the excellent Revo Uninstaller to do the actually clean up. It is free, easy to use and a a lot more powerful than the Windows XP control panel.