When I run into issues of "Strangeness" like this, I usually find that a quick run of Disk Utility "Repair Permissions" helps.

I run on a iMac, same spec as yours. ;)

Quote -  Poser 8 sr 2 
on a
MacIntel 2.4 GHz Core 2 Duo
 RAM: 2 gig
OS 10.5.8

Installed SR2 a couple of days ago I remember it running quite well with some (as promised) improved performance in the IDL department. Yesterday is not the problem.

Today, it crashes on start-up Everytime!  : (

Anyone have a similar problem or can guess what could be causing this?

Thanks for any help.