Windows Cleaning software

What software would someone recommend to clean windows up? My mothers computer had a virus on it that hit it pretty hard. It has since been removed but she gets a few errors at startup ect. that certain files(the bad ones) can't be found. What program that's kinda like Norton's WinDoctor are out there to use. I don't have Norton on her computer so I'm looking for something else.
Duck

I suggest Tune Up Utilities 2006. You can get a free fully functional 30 day trial and clean up her system for nothing. If you want to buy it it's $40. It'as a very good program, much better than the Norton.

ccleaner its free

i use a program called drive scrubber. by iolo ..i got it at newegg try www.iolo.com .when i bought it it was $70 it writes 1`s and 0`s to the hd ..i donot use any norton programs . avg anti-viros ,,zone alarm firewall is what i use both are good for online gameing

I'd second the recommendation for Crap Cleaner. Free and effective.

CCleaner's a great program, but if the comp's mentioning bad extensions at startup you might want to check the startup folder in the Start menu, as well as any programs that launch with windows (Start->Run->type "msconfig" without the quotes ->Startup tab).

Usually most entries in that list can be confirmed through googling. If something comes up random it may be a bad file/entry. Be careful with that list though as you could accidentally disable important files.