I have a part working interface using the ftdi chip (FT82U245AM), unfortunately due to personal problems I have as of yet been unable to complete the software, with this chip it's a parallel 8 bit interface memory mapped to the 8051.

A word of warning however, the ftdi chips are in a small smd package that requires some dexterity with the soldering, I've put mine onto an adaptor board.

Ftdi also supply driver software for the PC and again this seems to work OK.