Look around in that same section of your BIOS. There may be an "auto configure" option or something like that selected. You may have to change that before it will allow you to change it to 8x. If there isn't any option there then maybe your CMOS settings are just fucked. You might try clearing the CMOS and resetting everything to defaults. Or it could just be a shitty motherboard.
Another thing... I have a Saphire 9800 and I started getting the same VPU Recovery message a few months after getting it. It started happening in just one game and then progressively got worse, until it would randomly happen when just sitting on the desktop. I had done some funky shit to it like flashing it to a Pro and overclocking the shit out of it (stock cooling, bad idea). Anyway after setting the core and memory clocks back to the default settings and re-flashing it with the original BIOS I still would have those problems from time to time (though much less frequently). I tried everything with drivers and software that can be done, including formatting and installing Win2k instead of XP. Still had the problem with Win2k. Anyway, long story short, the last thing I tried was to use the same utility I used for overclocking to reduce the clock speeds to just a little below their default values, underclocking it. That solved the problem and I haven't seen any of those error messages since. This thing is sort of a "budget" 9800 and has a really dinky heatsink/fan on it. It was getting up to like 44 degrees, maybe a little more. So I think the problem is heat related. I plan to get some better cooling on it and then try overclocking it again later. Anyway, the program is called Rage3dTweak and you can get it at
http://www.rage3d.com/. Might be worth a shot.