I assume you mean AUDIO receiver. Your HTPC can play to PC speakers, which generally have built-in amplifiers. Should you wish to play thru conventional home audio speakers you will need and external AV Receiver or amp to drive them. The audio output from a computer is insufficient to drive speakers directly.
Good luck with your project. I think you will find it is a bit more complex and frustrating than you might imagine, assuming you wish to use the HTPC for TV, Video and music. You might want to spend some time reading at AVS Forums in the HTPC section to see what you are getting into. Not trying to discourage but like most computer related activities it is not always simple to achieve your goal.