You have quite a few options when it comes to getting media from a PC to your stereo receiver.

Here are the results for a search on "digital music server" to get you started:

http://reviews.search.com/search?part=&q=digital+music+server

One other option that I am going to pursue is the use of an XBOX 360 as a media extender. Using either Windows XP Media Center Edition or the free Windows Media Connect app for Windows XP, you can stream your photos and music from your PC to your XBOX 360 (either wired or wirelessly).

Regardless of which server/streaming device you choose, just make sure that whatever home theater receiver you buy has the proper connection.

For example, many music servers use RCA connections or optical audio jacks. As long as your home theater receiver has one of those jacks available, you should be all set.