Error at full memory-usage

[Lemmy]

Sometimes in some games my G400 32Mb DH quits to desktop without any errormessage. I can reproduce this when i make the 3d-Mark 99 test and choose the texture-memory-test for 32 MB. Then the programm quits to desktop. In dualhead-mode it quits at the 16 MB-test.
(because the memory is splitted: for each monitor 16 MB).

My Specs: P2-400 AsusP2B G400-32MB-DH 256MB-Ram.