Hmmm... very unfortunate he won't help you now. However, I'll take whatever time it takes to fix this problem with you if I can. I've been known to spend weeks helping people on this website, so I don't give up very easily as long as the OP doesn't.
One of the problems with downgrading a laptop from Vista to XP is that a lot of times the correct drivers aren't available. Many OEM manufactures (like Dell, HP, etc), don't supply downgrade drivers leaving people to forums and research to find how to install XP... not to mention the frustration they go through. Fortunately though, many succeed, and leave trails searchable via Google.
The correct way to install a Windows OS is... (I've stated this all over this website and I did it again just TODAY
)...Install the OS
Install the SM Bus controller driver (CHIPSET DRIVER)
Install all other drivers in any order
Now the situation is... we don't know if this "friend" of yours installed the OS in the above order. If he didn't, then it may explain why you're experiencing the problems with both the camera, and your usb hubs. You didn't mention the hubs before, but now that you have, it may be why the cameras not working (ref my last reply about it being a "usb image device").
There are several options available...
Research and fix the USB problem... and hopefully fix the camera at the same time
Since this is a brand new install, I'm going to guess you don't have much data on this computer right now. Do you?
Also, do you have the XP install disc in case you have to try a repair/reinstall?
Lastly for now, can you post a screen capture of Device Manager. If you need a screen capture software, there's a link to Printscreen in my signature.