“An engineer doesn't use a sledge hammer to crack a nut” as Steve said on other post (see stabilized platform).
If I correctly understand you must to call your 8051 based project from an ISP. Why to not write a cgi (can be perl, asp etc.) on the server that makes the call (I’m guessing you’ll have more than one location to call) get the data and respond to the client’s browser. In that mode you can implement a proprietary protocol between cgi and 8051, with some advantages: easy to test, less data to send/receive, cheapest system (perhaps that calls costs some money).

Think about

PS I was founding somewhere a nullmodem.inf driver (usefull for connecting the PC with the 8051 board and get the data on browser if you still want to implement a TCP/IP). Probably is at home.