I have Xp Pro on a HP laptop it runs a little slow it is not terrible.
Besides the specs which I will skip, Always running a firewall with antivirus-malware-spyware software is A MUST at ALL TIMES while CONNECTED to the net.
Buy your software, you will obtain more value and use.
Some antivirus-malware-spyware software is more user friendly AVG is a little lacking, Trend Micro is better, Norton can be a pain, McAfee can't say I haven't use it recently, Ad-Aware SE Personal is useful, use Disk Cleanup, Disk Defragmenter, look for some registry maintainance software.
A large number of losted shortcur connections can be a problem.
Do Not load a lot of FONTs, having a lot of windows opened at once is a problem - I locked my computer up last night-I had 47 Internet explorer windows opened and a few other things.
Backup ALL and I mean ALL text files, music, HTML, Photos, and other USER data storage files BEFORE reinstalling windows or Formating drives.
Delete on a regular bases file cookies, History files, MAYBE Temp files.
Do NOT run any computer or OS with a low amount of drive space, try to keep 30% clear,50% is great. If you visit crap sites expect problems . DO NOT open or download E-Mail from persons or locations you do not know, dump it - trash it UNOPENED.