YES, try the CS8900/CS8900A from www.cirrus.com. This chip contains everything you need except a 20MHz crystal and the interface to the "www" (some caps resistors and induktiv couplers at all less than 12 parts :-))

Search for the applications notes for connecting the cs8900/cs8900A to 8-bit devices. an-112 i guess

the schematic is too easy and the rest is software.

you can get drivers for windows (ce) linux .... (sorry no 8051) but if you or somebody has some sources for ipx/spx and/or tcp/ip please mail it to me, i would be very thankful.

any questions left ?