USB to serial adapter are suppose to do the same job as a regular serial port. There's no USB PICSTART. so i figure it's really suppose to work as well.

usb adapter available :

melabs http://www.melabs.com/products/accessry.htm.
SfCable http://www.sfcable.com/Merchant2/mer...ROD/72/UB30-40
Sewell Direct http://sewelldirect.com/USBtoSerial....ch_type=search

A search on Google can give you also many other place.