Just uninstall any programs you do not want.
Then run Ccleaner like said before
You can then go into start / run / msconfig / startup and disable any programs that you dont want to start when windows loads (helps boot times)
Then start / control panel / system / advanced / performance / visual effects , select Adjust for best performance . It takes away some eye candy.
Want to strip it more ?
Turn windows theme to classic , taking away more eye candy.
My personally take performance over eye candy any day.
Now defrag and do so once a week.
(locations of settings were for XP ; im sure vista is close enough to figure out)