Have a good desktop I built a few years ago sitting around with Win7 Pro on it that I am thinking of turning into a HTPC. Figured I could just get an HDMI cable and plug it into the TV unless anyone had some better ideas?

Figuring it would be used for Internet and watching movies that have been copied to the HD.

ETA - The movies would be the digital versions of ones I own legally, not illegal rips

Depends on what you'll be playing on the home theater - you want your platforms to be supported properly and well, so if you play your stuff off websites that require flash or something, you'll pretty much have to stick to Windows or OSX.

For just playing movies, linux variant of some sort will be fine. For access to things like Kodi, probably an android version.

I have Roku, which is what I watch the most, and XBox360 and PS3 (yes, I still haven't upgraded) can do most of what the Roku can, including playing movies and accessing Netflix - but the Roku is easiest and optimized for those tasks. I also have a full-on Mac-mini running OSX for some stuff I watch online through service providers which require current Flash as a player platform.

I've also got a Chromecast, so can just cast from a notebook PC or desktop directly to the big screen.

I did the same thing (on Win7), until I discovered Plex

If you have a smart tv, Roku, or Chromecast, just set up the desktop as a Plex server, stash it in a closet somewhere, and be done with it.

Win 7 is fine. Run PLEX on top of it and store your inventory on it. If you want, you can keep it outside your HT area and run a nice, quiet Roku with the PLEX client.

In case anybody hasn't mentioned it yet, forget the htpc idea, setup a Plex server and get a roku.

I would use kodi if it's just going to be playing the local files connected to a tv. I have messed with it a little bit but I prefer my Roku and a NAS Plex server. It is much easier to use with the remote.

Downloaded Plex server and plan on trying it out, now just need to find the time :)

I currently record and serve recorded TV to Amazon Fire Sticks running Kodi, using my old Win 7 HTPC, running Kodi and Argus TV.

Honestly, it should work for your purposes, as well. My ripped media is on a unraid server and also plays through Kodi.

poped in here to mention plex.

Just built a FreeNAS machine to specifically run Plex.  Rokus on all the TVs.