Slower evening internet speeds on Vista than XP

Hi,

My ISP is AOL and the internet speed drops from 7Mb during the day down to about 1Mb at night. That's just because AOL's like that on non-LLU. That's a different matter however.

During the day, my Vista machine and XP machines run at full speed. But during the evening, my Vista machine drops to about 0.7Mb (on average) but my XP machine tends to maintain a speed of about 1.5Mb. I know that doesn't sound like a massive difference, but when you have speeds that slow in the evening, it does make a difference. For example, iPlayer often works in the evenings on my XP machine but not my Vista machine.

I experience the issues even when both machines are connected to the router with a wire, so it's not a wireless issue. It doesn't matter what browsers I use either - it definitely seems to be an XP vs Vista thing.

Could anyone please help me sort out what might be going on? It's weird because it's only during the evening slowdown that the difference between the machines is obvious.

Just to put this into perspective - my XP machine (on a wired connection) is running at 3.1Mb. My Vista machine (on the same wired connection) is running at 1.5Mb. The ping on the XP seems to be slightly higher too.