There will always have to keep patching via windows upate, but SP2 is the latest service pack.
When I tried upgrading to SP2 after using XP for about two years it was real buggy, I had to restore from the ghost image I made before upgrading.
Later when I did restored from an even earlier ghost image and then upgraded and it worked great.
If you willing/able to backup your system first, then try SP2.
If not then learn how to backup your system first.