Dana, I'm not particularly tech-savvy, but I have the following set-up that works well for me.
First of all, I bought a mini-PC that basically functions as the media center. I have Zotac ZBox but I imagine there are a number of probably cheaper options. I have this connected to my router. My router also has connections to my TiVo and my desktop computer via an eternet cable.
The mini-PC output then goes to my receiver via one of its HDMI ports. The receiver is also connected to my Blu Ray player and my TiVo and output from it goes to my HDTV. Provided that your TV has enough HDMI ports, you don't really need the receiver, but the stereo sound you get from the receiver is nice. Through my Receiver remote, I control which screen I get on my TV screen -- TiVo, Blu-Ray player, or the mini-PC. When I go to the PC option, it basically gives me a desktop screen and allows me access to all the media from any of the computers in the house connected to the router via the Home Network. All my media lives on my desktop and I can stream it directly to my TV this way. Although nowadays, I'm too lazy to do this so end up watching a lot of media on my android tablet (they have some sweet applications that let me stream everything from my desktop, easy as pie.)
There are probably simpler ways of doing this though. The back of my media center looks like the aftermath of Tentacle Monsters Apocalypse and it's not pretty.