Unable to run windows update

So as usual I'm not really sure where to direct this question but homebuilt systems normally nets me an answer. I have a toshiba laptop and a dell 8110 desktop off the same network. The laptop is running windows vista or 7, I'm afraid I can't remember now. The dell is still xp home. I'm just cracking into the desktop to clean off viruses but it's been slow going. The laptop had no security installed at all, on arrival windows defender would not load and updates kept getting an error indicating server busy or unable to access network. I cleaned off all the viruses I could find with AVG 9 but no change. A search online yielded a few things to try but still no luck. Now working on this desktop I have the same error trying to run updates from over a year ago, the latop had not run any since october of 09. I am assuming they have either the same network setting error or virus gumming up the works but I haven't been able to find it yet.

Could anyone point me in the best direction to look short of reinstalling windows. I did manage to get defender working by deleting the registry key stopping it on the laptop. Thanks in advance, more info can be provided if you need it. XP is SP2 on the desktop.