Forcing refresh rate in Mac OS / Windows?

I'm 1000 times sorry for doubling this post, but maybe somebody in this section can help me... Yet 1000 times sorry.

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Configuration: Mac Pro (2008, 8800GT), Mac OS 10.5.3 & Vista x64 (via Boot Camp, latest graphics drivers from nVidia for Vista x64), 2 x LaCie 120 monitors.

Problem: While booting in either OS, monitor went black with a bouncing icon ‘Input not supported’.

I’ve more or less resolved the issue in Mac OS, but booting into Vista remains a trouble.

Problem is that OS is forcing a higher refresh rate than is supported by my LaCie 120: 75 MHz (or more) instead of 60 MHz.

After the boot-up is completed, interface loads and everything is fine. But if there is some error during booting, the screen remains black with this bouncing icon ‘Input not supported’. Thus I have to find a way to change the refresh rate on the system boot stage.

Is there any possibility to force the right refresh rate (command line, Terminal etc.)?

I’ve googled this issue, but so far none of the remedies have helped.

Thanks,
sash