I've had this setup for a long time now, I just rewired another room and wanted to omit the Mac audio cable.
This is the USB extender I use:
http://sewelldirect.com/usbextenderhub.asp
Don't get it though. There's no power adapter and I've had issues with it. That same website has newer and better ones (and cheaper).
For computer monitors, check here:
http://search.ebay.com/search/search.dll?from=R40&_trksid=m37&satitle=cat5e...
The black one you see listed a lot are the ones I'm using. They work with most equipment. Not all. Some monitors don't like it. Some graphics cards (port 2 on an X1900xt for example) don't like it.
Gefen and others make much more expensive extenders. But people have similar problems with those as well. For me it was worth testing the cheap ones first.
Sean