Understand that I run linux, and can point you towards clues -- also, when
you describe 'graphical glitches', that probably doesn't tell us enough...
ie; exactly what graphical glitches are you seeing, and how do they manifest
themselves....
Further here, I -think- I saw one of the codeweavers devs (Stefan) post a
comment saying there were a few issues with snow leopard, which they hope
to solve in an upcoming crossover-games release - if the problem you're
seeing is related to one of these issues, then probably all you can do is
sit and wait for the new releases...
Of course, feel free to submit a support ticket on the graphical issues you
are seeing -- it is after all the 'official' support system here. Alternately,
you can email info@codeweavers.com describing the problem, and someone will
get back to you ASAP...
Regarding clues or things to try, (and this may be arduous), you can have a
read through this lot related to Mac OSX 10.6.x issues...
http://www.codeweavers.com/support/tickets/browse/?s_subject=snow+leopard&search=Submit+Search&s_parent=1
Hope this helps!