Back in the day, Symantec Win Doctor was the bomb, however, required you to pay for it, and anymore I don't like Symantec much. I use AVG for anti-virus, Ad-Aware for spyware/adware, and CCleaner for OS cleanup etc... All of these programs have one thing in common, they are all freeware, and I have found that they perform as good or better than those programs that are bought.
However, no registry cleaners work as good as a re-format and fresh install of everything. Which requires backing up data, programs etc. so that there isn't any problems. As far as activation goes, you shouldn't have to talk to anyone, you can connect through internet and send everything electronically, and as long as you didn't change your processor or motherboard there shouldn't be any problems, and certainly everything can be done over dial-up or broadband internet connection. No need to call, however, if you do call, it is automated, and only time I had to speak with someone, was when it wouldn't accept the OEM number for some reason (everything was taken care of in less than 5 minutes with CSR though).
Of course, if you've got some sort of hacked version of XP, that might pose a problem, but nothing $100 can't fix, by buying a legal copy.......