Mmm. There does seem to be a problem with that map on the N900. Doesn't crash on my Debian Lenny desktop, using the same pk3 file. Workaround is to keep playing the map until you beat it without crashing. I did find that if I kept replaying it a number of times in a row it seemed to last longer before crashing, until in the end I managed to beat it. After that, you can at least access the higher tiers.