Sounds like you've got a system that uses the slower PC133 SDRAM instead of PC2100 or better DDR or PC800 or better RDRAM. This can do some serious damage to the overall speed of your system. Unfortunately, the only way you can really use the other memory types is to buy a new motherboard and memory, and memory is kinda pricey at the moment.
Also, these site tend to tweak the system for maximum performance with certain BIOS settings.
In some cases, the overclocking of the CPU and/or graphics card is used to achieve those awesome results.
The operating system and drivers can also play a major factor here as well.
Lotsa variables.