"FTDI have a serial to USB chip which might be worth looking at."

If I understand the original post correctly, the requirement is to implement a USB host - ie, the equivalent of a PC which will drive the USB printer.

Although the FTDI parts are great, and I have frequently recommended them here and elsewhere (use the 'Search'), they implement USB peripheral functions - therefore, they are the wrong end of the link for this application. :-(

I would suggest that a USB host is not something you want to try implementing on an 8051 (or even an AVR).