Hi...

This One Is Not Really 8051 Topic...

The IR Led Transmitter works just like a regular LED,
it needs about 10mA to 20mA (I use 15mA) the voltage will
be consumed by default (make a current source) and should
be about 2V.
the receiver should be a transistor, which its hfe changes
according to IR Beams it receive. usually hfe is higher
when it receive an IR beam.

Good Luck..