I just installed UT2003 on a Mandrake9.1 box. I've got up-to-date display drivers and version of SDL libraries.

I fire up UT and this is as far as it gets in the trace:
Backtrace:
[ 1] ./Core.so [0x409c8c32]
[ 2] /lib/i686/libpthread.so.0 [0x40d955ce]
[ 3] /lib/i686/libc.so.6 [0x40b583b8]
[ 4] /UT2003/System/OpenGLDrv.so(SetRes__19UOpenGLRenderDeviceP9UViewportiiiii+0xd0) [0x4379e910]
[ 5] /UT2003/System/SDLDrv.so(TryRenderDevice__12USDLViewportPCwiii+0x11e) [0x43769806]
[ 6] /UT2003/System/SDLDrv.so(OpenWindow__12USDLViewportUiiiiii+0x223) [0x437687d3]
[ 7] ./Engine.so(Init__11UGameEngine+0x1043) [0x40259753]
[ 8] ./ut2003-bin [0x805513e]
[ 9] ./ut2003-bin(main+0x296e) [0x805813e]
[10] /lib/i686/libc.so.6(__libc_start_main+0xc7) [0x40b457f7]
[11] ./ut2003-bin(ValidateCDKey__Fv+0x49) [0x80511f1]
Signal: SIGSEGV [segmentation fault]
Aborting.

OK, so the first thing you think is :I typed the CD key incorrectly" ... nope, re-installed and did it again.

Anyone got any clues for me?

is your graphics card an nvidia card?

i've heard that ut2003 for linux is intended for nvidia cards only
i've seen it on an ATI radeon7500
and it was awful and crashy

other than that
sorry, i have no idea
it works just perfect on my mdk9.1 sys

after reinstalling, did you erase this directory .ut2003?
/home/user/.ut2003