Just want to watch shows already in my collection, no recording, recommend software?

I have a laptop with a 2ghz Turion processor, 3gb ram radeon 3200hd video card. I'd like to hook it up to my hdtv directly or through the 360 and turn it into an htpc. I can use my harmony remote to somewhat control the laptop, so that's a plus.

I have a vast library of downloaded and recorded shows in all kinds of formats(avi, mpg, mp4, mkv, you name it). Not interested in recording anything, just want to be able to watch what I have.

I do have a WDTV, which does most of what I want, except it doesn't handle DTS audio and some mkv movies.

What software solution is best for someone like me? Would like something that's easy to set up and can handle many formats. Thanks.

Ok thanks. When you say windows media center, are you talking about a direct hookup to the tv, or through a 360 or some other extender?

Will also check out playon and mediaportal

Thanks for clearing that up, much appreciated.

Another question. If I go with media center, will it let me forward/rewind my videos? I thought I read somewhere that the files have to be in wtv or some format specifically in order for media center to ff/rew. I'd rather not have to convert my collection if possible. Thanks.