(Forget the free in the title. I can't edit my titles. But if you do ahve any free games that are good for this, I'm welcome to here them)
HI people
So my brother has this ancient windows xp pc, and we were looking for some LAN games to play on it. We already have Serious Sam, C&C TFD, UT1999, Duke Nukem, Defcon, Blood and Nox.

We're looking for some other ones. We like FPS, Real-Time Strategy, Racing, Flightsim and RPG.
We like games in coop, but we do have deathmatches. Anybody got any good ones?

I've come up with a list of ones that look good:
Carmageddon
UT2K4
Freespace 2
Painkiller (does this have multiplayer?)

P.S. I'm welcome to donations of any good LAN games you have

I put at the top of my post to forget about the free bit.

I don't know how it will act on xp, but warsow is pretty good, though it apparently takes a little work to get lan set up.

Thanks. I actually already have Warsow and Xonotic, and they work fine on my PC, but I'm not sure how well they will run on my brothers. Worth a shot I guess.

This was one of my favorites BZFlag. Its a capture the flag using tanks.
It's open source so fits the free requirement.

And looking at the screen shots its come a long way since I played back in college (late 90's.)

Thanks BZflag looks good

We liked playing Darkstone on LAN. Haven't played it in years so it may be too dated by today's standards.

CoD: MW
Warcraft 3

CounterStrike 2D
http://www.cs2d.com/

Soldat, Nexuiz, Xonotic, Renegade X, Americas Army, Alien Arena, Fear Combat ...

http://www.freelangames.net/p/games-index.html
http://freegameslist.weebly.com/lan-games.html

I wish a long life to this game and community
http://www.desura.com/games/openarena

Just try it.

Thanks Guys. I already have Openarena, Soldat and Xonotix. fear combat looks cool though.

I can recommend Baboviolent 2 as a fun and accessible game to play when you cool down between longer sessions of RTS or RPG games.

It's a really simple top-down shooter, easier than Counter-Strike to get into, and it's free too!

Also, since you mentioned UT99, I can thoroughly recommend a game called Rune made with the same engine.
I Can't remember if it's a mod or standalone game, but if you can find it, I'm sure you'll have a blast with it's ultra-violent viking combat.

I used to play SOLDAT on the colleges LAN over 10 years ago

Quake III Arena is a lot of fun. Just fill it out with bots and have at it. A friend of mine and I used to do that and always had a good time of it.