Looking for USB-over-ethernet solution
I've not found anything that supports OS X as a the server, and Windows as the client.  The best solution I can suggest would be Belkins network USB hub or digi's AnyWhereUSB product.


http://www.belkin.com/networkusbhub/ - hardware share to win or os x
http://www.digi.com/products/usb/anywhereusb.jsp#overview - Hardware share to Win
http://www.virtualserialport.com/products/usb-over-network/ - Win/Linux - OS X coming soon 
http://communities.vmware.com/thread/77230 - Reviews
http://www.intellidriver.com/products_1.16.html - Win
http://www.usb-over-network.com/usb-over-network.html - Win
http://www.fabulatech.com/ - Win/Linux
http://usbip.sourceforge.net/#about - Linux/Win