1)well, from the looks of it, it would cost me some amount of money. as much as possible i would like to stick to what i got right now which is keil.

also, i only have one pc.

2)ok, this time, never mind the multiprocessor... just a single processor. what i wanted to simulated in particular is the serial io aspect of 8051.

is it possible for me to input values in the serial port during program execution?

1) if you are making a low volume project, why not use Cygnal, an ICE equivalent JTAG cost $99- $149 and you can run two on the same PC
If you are planning on high volumes, CEIBOs new software allow you to run multiple ICEs on the same PC.

2) Your message is confusing "simulated ... program execution" Of course you can during "program execution". I assume you mean while simulating.
To the best of my simulated knowledge (I hate simulators because they SIMULATE) you can feed simulated serial data to the simulated UART when using the Keil simulator.

Erik