Using widescreen for gaming?

Hi, new to this forum!

Tried to get an answer to my question with the search function, there looked to be a lot of relevant threads but all of them were "Sorry, this thread doesn't exist", so here I am.

To the problem. I'm thinking of buying a new TFT monitor soon, choosing between a 20'' regular resolution, a 20'' ws and a 22'' ws (all samsungs), but I'm concerned about having a widescreen as I play a lot of games (FPS, RTS etc), right now I'm going with a 1280*1024 17'' TFT and I think it's great. Have heard some stuff about widescreen and games, like old games won't work at all with them, and a lot don't support widescreen resolutions, and having regular 4/3 or 5/4 resolutions on a widescreen makes everything look a bit "fat" (the image streches out) Still want to have a widescreen as I watch a lot of movies, but not willing to sacrifice not being able to play games

I have another question about widescreen monitors, when having a "regular" resolution, why don't some monitors leave the sides out (make them black), like when doing the opposite thing on a regular res screen (watching a widescreen movie on a regular res screen)? Or maybe this function exists? don't know why I have got this idea because it's been bugging me a lot.

Basically I want to know: how do games work with widescreen monitors? new and old?

Cheers!