just need a photodiode and an IR led
you just need an IR Led for transmiter and a photodiode for reciver.
This way you can build the electrical interface of IRDA.
Next, you need to write a few lines of code yn your mcu for inplement a much like software uart. Main difference are that IRDA signals are Zero Return (ZR) insted of RS232, wich are Non Zero Return (NZR).
I've implemented IRDA in a PIC16f84@4Mhz and it works very well
Look at Philips Semiconductors for IRDA details.
good luck