Chances are that Dell BIOS is locked up pretty tight, with slim chance of an fsb change. Might be able to tweak it with software though, depends on the chipset I guess. Is it a slot 1 or a socket 370 P3?
I would agree with you. I had 2 Dell before and their BIOS are VERY simple and limited. Only the current high end are overclockable I believe but they are way too overpriced (can do a custom at a better price).
That why I left Dell and did my own custom build.
Anyway, would you see a big difference from 800 to 1000? And you can have a basic one starting at 379$USD. Must say that very low for light use.
I you find a way, let us know!