For what it's worth, the halflife2 forum on this site provides a good list of things to do (it's for a mmacbook, but it should work across the intel line of macs). However, I find the game crashing at seemmingly random points from a few minutes to less than an hour after starting up. Varous types of crashes occur, from sound failing, to hard lock, to dropping out altogether.
In this edit box, the cursor doesn't allow what I'm typing to fully show,l so I aplogize if it's a bit harder to read. Must be code that doesn't like firefox 2.
System: First gen intel imac, core duo, 1GB ram, ati x1600, 250 GB drive, 17" widescreen at 1440x900.