Dimension C521, Vista x64, 4GB RAM and voltage

Hey there,

I'm trying to run my Dimension C521 with Vista x64 and 4GB of 800mhz DDR2 RAM.  There are issues with this.  I've messed around with this a LOT recently and I cannot get it to work with 4 1GB DIMMS.  I get it to work with 3 1GB DIMMS but the board comes with four slots and the specs say it supports 4 GB so that's what I want to use.

The only thing I can find (after reading almost everything I can find on the internet on this subject) is that there is an issue with some motherboards and the clock of the RAM.  IT seems that you have to underclock the RAM to 667mhz in order to get it to work.  I'd love to be able to change it but there doesn't seem to be any way to do so due to Dell's ridiculous BIOS options.

I w

Can anybody point me in the right direction to one of the following:

a) a solution that doesn't include voltage

b) a software program that will adjust memory clock outside of the BIOS

c) an upgraded (perhaps grey market) BIOS for this system past 1.1.11 that enables advanced clock functionality

As an adder, no program that I have used can see the voltages on the motherboard, not nTune, not Speedfan. Not anything.  I have also tried the MS patch that deals with this problem to no avail.

Please help.

thanks

Lucas