3008WFP doesn't display boot menu on MacPro

I've been working on setting up a MacPro at work (I set up faculty members' computers at the university I attend), and it's just about good to go. It's set up to run both OSX and Vista 64 through Boot Camp.

So here's the issue... David (the faculty member) has a three monitor setup, with two 24" Samsung SyncMaster 215T's set in portrait on the left and right, and a 30" Dell 3008WFP in the middle in landscape (all are using DVI-D). The Dell is of course set as the primary display. When the computer boots up, rather than showing the off-white Apple boot screen, it's just a black screen. The monitor recognizes the input because the status light turns from amber to blue. Once it gets into an OS all three monitors display the OS appropriately.

This is an issue since David needs to be able to select an OS when he boots up, otherwise it will always go with the default.

I hooked in just one of the Samsungs via VGA, and the boot menu appears just as one would expect.

So the culprit is obviously the Dell. I went to dell.com and installed the Vista driver for it (looks like there isn't a Mac driver available?). I've tried shutting it off and then on. I know the connections are secure and the cables are good. I've tried flipping through the monitor's different inputs during boot up as well. I'm not really sure what else can be done.

Any ideas?