One quick thing you can do if you don't find a decent utility program is to go to Control Panel...Add/Remove Programs and look at the list that XP knows about. You will get a cursory glance at the largest consumers of drive space right there! You may have a welcome (or unwelcome) third-party software that installed itself quietly and just sits around taking up space.

Run a defrag as well to free up drive space.

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2009 ML350 (106K) - Family vehicle
2001 CLK430 Cabriolet (80K) - Wife's car
2005 BMW 645CI (138K) - My daily driver
2016 Mustang (32K) - Daughter's car