Here's my advice: Get the GOG.com versions which are easier to mod. Install them somewhere that isn't Program Files so they aren't write protected (like C:\games) Apply this patch for Thief 1 and this patch for Thief 2.

Last time I checked in on Thief 3 modding there were some patches to make it more like the original (like getting rid of body awareness) that actually almost broke some of the basic gameplay (blackjacking dudes.) I'd advise just playing Thief vanilla unless someone has a better idea which means you can get it from either GOG.com or Steam.

Oh, I do want to play them, I just haven't gotten around to it. And yep I got the Gogs.

@beachthunder:

Cool.

Those patches I linked to have no only some good graphical updates and fixes but also the new engine update made from leaked source code that makes the games run like butter on new machines.

@august said:

The only mod for Thief 3 I would advise is John P.'s texture pack. It's really good.