Yeah, I would tell them to have a fresh OS install done. If the computer will run it, I'd suggest to them to get Win7. A dual-core 2.4GHz+ with 3GB+ of RAM will do. They sound like people that install a lot of apps (whether they end up using them or not). XP gets conjested easily and will bog down. Even if you uninstall all the apps that don't get used, it's not much help. Plus all the possible shit that could be on the computer from years of Internet use.
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Never argue with an idiot. They drag you down to their level and then beat you with experience.