Hi Angline,
I would make a recommendation that you break this project up a little first. See if you can establish serial communications between your 8051 and your PC first--I'd start off using hyperterminal instead of Matlab, and I would send known data up from the 8051 instead of trying to work with an external data input to the 8051 (ADC, digital inputs, etc...). Once you've established serial port communications between the 8051 and the PC, then work on using MATLAB as your PC application. Once that is done, work on gathering the actual data of interest. Best of luck.
Josh