Grey screen after installing updates

After holding off for a while, I just installed a number of system updates on my MacBook and when it did the necessary restart it got stuck on the grey booting screen. I'm on a four year old MacBook running 10.5.8, and I've never had problems like this before.

Based on a couple threads I've read it sounds like this could have something to do with faulty off-brand RAM, however I don't believe I have any installed (at least I certainly don't remember installing any, but hey, if I did it would have been four years ago. So maybe I did?)

You should also know that before the install, I was cleaning off my computer and threw away about 12 gigs of files. I was meticulous to make sure I didn't throw away any system files (it was predominantly apps, old video renders, music and photos), however I did delete a couple preference panes that were associated with applications. I also (and I would be horrified if this is causing the problem) deleted the entire iTunes folder.

When I boot up, I get the grey screen with the spooling circle. Booting with a NV/PRAM clear (command-option-p-r) does nothing, nor does a safe boot (shift). If I hold option during start up to use Startup Manager, my OS X volume shows up, but if I select it as the boot volume I (unsurprisingly) just go back to the grey screen with the same problem.

I held down D during start up to run the Apple Hardware Test and the results were "No trouble found" so I'm hoping it's not a hardware issue.

I'm on vacation (a wonderful time to go through this!) so I don't have any of my install disks with me.

Any ideas?