Advising someone who's unemployed to buy even a used PC is not being very realistic at all.
XP is still loved and used by thousands of people worldwide, and by the time it got to SP3 it was stable and reliable, plus it's RAM requirements were very modest, unlike Vista that followed it (and that wasn't Vista's only problem by a long way).
Ditch Vista and use XP my friend. Don't worry about Microsoft no longer supporting it. Just ensure you've got a good antivirus installed, keep the Windows firewall on at all times and you'll be fine.
Running an old OS could become a problem if you buy any new software or hardware, but you're unlikely to be doing that if you have no job I expect. Enjoy Windows XP and remember you can get all the...