I think my comp has a virus?

I just bought this computer second hand. It is windows xp. I do not have the operating system disk or I would probably just wipe it completely clean and hope it takes care of the problem. I KNOW it has a virus(s). When I run task manager and look at the processes 'svchost.exe' is listed 6 times. A few has 'system' listed after as well as 'network service' and 'local service'. They seem to really suck up a lot of the mem usage. My webpages keep getting hijacked and redirects me to various search engines. I have looked through support pages and googled 'svchost.exe' and says I need to clean and repair my registry. There is so much freeware out there and I do not trust anything at this point to actually fix my computer. I don't want to keep buying different programs that do not work just to have to remove it from my computer because it interferes with the new programs. I am using AVG and Windows Defender and umed that should protect me but they are not even detecting the problems so any suggestions as far as finding and manual removal of this virus(s)? Should I just try to get a operating disk and completely wipe this computer out?