Mac Pro :: Locking Up - 8 Minute Startup?

In the past couple of weeks I've been having issue with my workstation locking up, the first couple times it only happened when activating expose, I'd have a bunch of apps open(final cut, photoshop, bridge, entourage, +) and it would freeze when I activated expose when all the windows were shrinking.

In the past week though it's been happening out of nowhere, still with final cut and other various apps open but no warning, but now the screens don't freeze they go blank, but the tower doesn't sound like it's powering down or doing anything besides the norm. It almost seems like a video card issue.

However just minutes ago it happened again, screen went blank(thank god my final cut autosaves every 5 minutes). Did a hard restart and logged in but after my desktop picture loaded nothing was happening, spotlight was up in the corner(not the whole menu bar) and mousing over spotlight showed a beachball. Another hard restart and same thing, so I just let it sit for a while and after 7-8 minutes of sitting there with just my desktop image the rest of the os finally loaded. I was getting worried as I have deadlines and one of them is tomorrow. This machine is usually in use monday-friday 9-5.

Specs:
OSX Tiger 10.4.11
quicktime 7.3.1(can't upgrade to 7.4 or 7.4.1 because it causes issues with after affects rendering & were getting a Red cam which the latest quicktimes don't work well with)
Mac Pro Quad Core 2.66
5GB 667
ATI x1900 w/ 2 monitors(1920x1200 & 1280x768)
500gb system drive
2x 500gb drives in mirrored software raid
320gb storage drive

Running mostly Final Cut studio 2(latest updates) & adobe design premium cs3 and occasionally after effects cs3

Anyone else having this issue or have a solution?

Also our other editor has noticed his station(almost exactly the same but with 8gb ram) has been running a little slower than it should be as of late.