Mac Pro 2008 Display issue Nvidia GTX 285 & ATI 2600 XT with 4 Screen

Thanks for reading. I hope this is something which is solvable.

I recently bought an Early 2008 Mac Pro Eight Core 2.8. I have 4 monitors hooked up to it via an Nvidia GTX 286 (2GB version) and the ATI 2600 XT which came with it. Quite frequently, on start up and after the chime, the screens all show the blue default background colour and freeze for around 30-40 seconds. After that the boot continues as normal and the desktop appears.

Now, if I drag something from the lower monitor into the upper monitor (they are set up as one row of one and one row of 3 - a sort of upside down 'T') the item stops at the upper edge of the lower screen and finder freezes for a while. I can't drag anything into this screen.

This doesn't happen every time I turn the machine on but it is very frequent and the only way to fix it is to restart and hope for the best.

The screens are all 19" VGA monitors - all the same bog standard Samsung monitor at 1280x1024 75hz. The main screen (with the apple menu bar) is attached to card 1 (GTX) in port 1. The operating system is snow leopard 10.6.8 and the GTX drivers are installed.

Is there some issue with using multiple screens on a 3,1 Mac Pro?

Thanks again for reading this.