My motherboard states that it is compatible with either PC100 or PC133, and by default, was shipped set at PC100. The booklet states that if the RAM is PC100/133 compatible, then the setting in the BIOS can be manually changed from 100 to 133. The RAM I have states the same thing, it is compatible at either PC100 or PC133.

The only place I have found a value of 100 in the BIOS is at the "CPU Overclocking". I have not worked with overclocking in the past, but, is this the setting in question? THANKS.

Setting that value to 133 will have very nasty results. You can increase that value a bit to get some minor overall performance increase (both CPU and memory) but 133 will mean an instant crash.

It would help if we knew the exact type of your system BIOS.
You have to look for some setting about memory clock.

Fore axample in the BIOS setup of my computer there is a setting under CPU setup called "DRAM clock" that can be set to either "Host CLK" or "HCLK+PCICLK". First option sets the RAM clock to 100MHz (system bus), second to 133 MHz (System clock + PCI clock)

HI: As mentioned on my original post, the system is "already set" at 100, which is default. So I'm confused where you state that setting it to 100 will give nasty results, while in fact, it runs very good at 100, the factory preset.

What processor do you have and what clock speed is it running at?

If your motherboards FSB can run memory and CPU out of sync, you could set the FSB to 133 for the memory and be fine. However, most older motherboards did not support this, the cpu and memory had to run in sync. If this is the case, you will most likely not be able to use 133mhz FSB.

Oops! My mistake.. Fixed now.

I am using an AMD Athlon 1800+ CPU on a MSI motherboard. The system is a little over a year old.

in that case you should run it at pc133 so it syncs with your fsb