Reinstall XP
Use Acronis True Image or similar to create back-up - Image
Thereafter note installation of apps, major changes made etc
Periodically restore the last Image and re-install only what you realise works and want to persevere with
Update Anti Virus etc
Create a new Image
Keep the Images for possible future use.
If things go haywire or slow down restore the last 'good' Image and resume from there.
With practise it only takes a few minutes to create/restore an Image
At times before doing something I'm doubtful of I create a 'Temp' Image
Play about and if it doesn't suit or goes haywire - restore the 'Temp' Image
I rarely ever uninstall software simply restore an earlier Image
Normally I only install the OS once on a PC - It's easier to restore an 'early' Image - only takes a few minutes - Works for me
Lots of further tweaks to this process but that takes a bit longer to explain.