As I understand it, their little module (and the associated drivers) is intended as a "quick-start" to get you going with USB. For more "serious" work, you can attach an external "personality" ROM and, of course, write your own drivers to do whatever you like!

"Is FTDI an established/reliable source?"

Well, I can't answer that directly, but when I connected the module to my PC I didn't even need the FTDI drivers - it immediately appeared as a "D-Link USB Serial Port" (I have a D-Link Hub+Serial+PS/2 [1]).
I contacted FTDI, and the tech support guy (not called Fred!) said that D-Link actually use the FTDI chip

"but it'd be really slick if the FTDI part could be configured to appear as an HID/keyboard device."

Or you might try looking for a PS/2-to-USB device? implementing the PS/2 interface on 8051s has been widely covered - here and elsewhere


[1] 4-port hub + 2xPS/2 ports + 1xRS232 port.
http://www.dlink.co.uk/long_desc.asp?id=224