Svchost is a core Windows program that runs as a host process for services that use DLLs. It's having trouble reading and writing from memory, meaning that something has fucked something important in Windows. This would explain why websites don't work; the programs that control network traffic can't start.
Chances are that XP killed itself. Have you uninstalled/reinstalled anything lately?
I had a similar problem to this a while ago. It was a minor annoyance at first, and it got progressively worse over time. I traced it down to letting MSN load at startup. The only way to fix it is to reinstall Windows, because there's no way to know what processes are trying to access those memory addresses.
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