256 MB of RAM still won't do. I know from experience that, even with Linux and WindowMaker (and that means much less memory being used than with KDE or Gnome) deathmatch games are very sluggish at start (especially when you pick up weapons) and CTF is unplayable most of the times.
So I think
at least 384MB would be required, though I tend to believe that 512 would be more precise.
P.S.: Yeah, I'm usually as redline-low-end anyone can get and still play

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[later edit]: I also ended up upgrading for more ram

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