mad jew said:
Maybe take out the third party RAM for a while, and see if that helps.
Might also take out the first-party RAM

(Flashback) When I had RAM problems, it was my supreme good luck to have the @#$% hit on the motherboard-integrated RAM, which of course can't be removed.
I don't know anything about OS X's virtual memory system, but if it happens just a few seconds after you set the machine down, I wouldn't be surprised if the OS is at that moment writing memory contents to swap. Memory and hard drive would be my targets.
Check the console (in /Applications/Utilities) against the times of the panics. That might yield something helpful. Of course, the fault might trigger a crash so quickly that the system couldn't log it....
Check your free space on your hard drive. Check the hard drive in Disk Utility and see if any warnings come up (doubtful, but worth a shot). If you have the hard drive space on another machine, back it up or do an archive & install (they're nifty).
Boot it up using an Ubuntu LiveCD. I'm assuming that you're using a wireless internet connection, which won't work with Ubuntu (unless they've gotten that broadcom 43xx driver into general populace), but either way it should help narrow it down between the memory and the hard drive, as a LiveCD will cheerfully fill up all your memory but not touch the hard drive.
Another thing: how long is your screensaver set for? Nah, it shouldn't be graphics, since you said that this was happening quicker and quicker....
Try ripping out the airport card too. I dunno how there'd be anything wrong with it, but in general removing anything that can possibly be removed is a good idea when troubleshooting.