connecting hardware to my program

I want to know how to connect my own circuits to my comp so that the software i write can communicate with my circuit.
For example i have the circuit of my remote for my remote controlled car. I have transformed the remote into a pcb with slots like a normal vedio card. I want to know how to connect my hardware to my comp and to which ports. And also how to use C++ to control those ports.
Thanks[FONT=arial][COLOR=crimson]

What OS are you using? It gets more difficult the higher up you go.

DOS - access it directly using in & out
W9x - you may need DDK (download from MS site)
NT/2K - you will need DDK (download from MS site)
XP - you will need DDK (buy from MS)
Linux - don't know

You can always use 9x in DOS mode.