Things to look at first:
1. Program run at startup (start>run>msconfig, go to startup). Make a note of the current setup. Disconnect from Internet. Disable everything. Reboot. Gradually go back to the original status. See where it runs out of hand.
2. Services running at startup. Start>run>services.msc. That's more specialistic work. Comparing with a PC that boots normally is doable for everybody, however.
Kees
For a friend:
XP Home takes @ 20 min. to fully boot before he can do anything.
Message he receives is something like "virtual memory too low".
I don't have further details about his system. He will email them
later.
Is there somewhere he should start looking?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic