it supports all LGA775 CPUs to date. That runs from relatively cheap Celeron Ds through to the uber-expensive Pentium XE 840, so it's support for CPUs with 533MHz, 800MHz and 1066MHz system bus speeds and, importantly, for the new wave of dual-core CPUs. The i955X Express, incidentally, doesn't support 533MHz system bus processors.
Maximum RAM will be limited to 4GB