browsed around a lil bit, checking if some games are open sourced, so so far


ROTT (Rise of the Triad)

theres a few linux ports floating about
http://icculus.org/rott/ (open source is downloadable from here)

WOLF3D

theres a iphone open port dont know if anything can be done with it.
http://www.joystiq.com/2009/03/24/ca...in-for-iphone/

HERETIC

apprantly source code is out there, but now sure whats needed under the GNU license, not looked into it greatly
http://www.fsf.org/blogs/community/hexen-and-heretic

Tomb Raider aka OpenRaider

seems like the most likey one.
http://openraider.sourceforge.net/

EDIT: Lol, just after posing i find this...

http://www.classicdosgames.com/misc/source.html

most of the above are listed here, with source download...

FreeC&C

http://home.mayn.de/comrad/freecnc/ (Flame tanks ftw )

OpenJazzDC Jazz Jackrabbit

http://www.dcemu.co.uk/vbulletin/showthread.php?t=17655

OpenTyrian

http://code.google.com/p/opentyrian/

OpenUT

http://openut.sourceforge.net

TA Spring Project (Total Annihilation)

Being recreated in complete 3D and will be fully open source, might be a little to much though..

http://www.dmoz.org/Games/Video_Game..._Annihilation/