Xps 410 memory upgrade

First thanks for your time.

I have a Dell XPS 410 here are the motherboard specs.

Socket Type Socket - T (LGA 755)
CPU Support Pentium 4 from 631(3.0G) upto 661(3.6G)
Pentium D from 920(2.8G) upto 950(3.4G) and 955(3.46G)
FSB Support 800MHz/1066MHz
Chipset(Northbridge/Southbridge) NVIDIA nForce 4 SLI (NVIDIA C19/MCP 55)
Upgradable BIOS 4Mb Flash EEPROM
Memory standard 533 / 667DDR2 (240 pin)
Number of memory slots 4 slots (populate in pairs for dual channel)
Memory Modules supported 512MB, 1GB, 2GB
Max memory supported 8 GB (using 64-bit OS)
Audio controller Sigmatel 9227 on High Definition Audio Interface
Audio specifications 24-bit ADC, 24-bit DAC
7.1 channels
~90 dB signal to noise ratio (tested)
Expansion slots 2-PCIex16
1-PCIex1
1-PCIex8
3-PCI
Internal Connectors 1 - ATA100 channel (upto 2 Devices)
6 - SATA || (3.0 Gb/sec, NCQ with compatible drives)
SATA RAID 0/1/JBOD supported
1 - FDD channel
3 - PWM controlled fan headers (with compatible fans)
2 - USB 2.0 (USB ports 8 & 9)
1 - IEEE 1394a
1 - Front panel (audio, PWR & HDD LEDs, PWR button)
Rear panel connectors 1 - 10/100/1000 Mbps Onboard LAN (RJ-45)
8 - USB 2.0
2 - PS/2
1 - Serial (COM)
1 - S/P DIF out (optical)
Physical Form Factor 7 - slot full sized BTX standard (12.6" x 10.5" )

So I know that 1.8v RAM will work in my PC but all the RAM I find that is PC2 6400 at 1.8v can only have a Cas Latency of 5. I want to run RAM that have a Cas Latency of 4 but they all require 2.0v - 2.1v. I have looked into my Bios and on the forms and found that I can not change the voltage through the Bios. Will my pc auto set to run the 2.0v - 2.1v or do I have to stick to RAM that operates at 1.8v.

Also is it possible being a noob that there is a way to change the voltage and i just have not found it yet?

Thanks for your time and help.