Bios Mods -The Best BIOS Update and Modification Source

Is there any way to somehow mod the BIOS to actually read and use ram that is slower then what the manufacturer requires. I ask because i Have about a hundred HP7800 SFF that will not work with pc2-3200r-333 or PC2-4200U-444-A0, but will work with pc2-5300U-555. With the 333, and 444 ram installed the computer just beeps and will not even post.

Thanks in advance