New life for old XP

I am on an old toshiba, XP, Avast free and on the internet. I also have Ubuntu on another HDD I move around. My wife uses a hp laptop that came with win7 and after malware, updates and all the problems I installed ubuntu with firefox as a browser. She does all her stuff on it, ordering, pays bills, facebook/farmville, we share a netprinter and some files via the in house network.
I will eventually have a problem on the XP machine, who knows.