I stumbled upon an interesting post on a Windows Vista blog site regarding the posted memory requirements for the various Windows operating system flavors. It seems that Windows HPC Server 2008 actually requires less memory to run than the standard version of Windows Vista. Windows Vista requires *at least* 1GB of memory [except for the 'Home Basic' version which will run on 512MB]. Windows HPC 2008 can run no 512MB.
Granted, these are minimum values. The article also goes on to point out that HPC 2008 would prefer to run with 1.5-3GB in a 32bit environment and greater than 4GB in the 64bit flavor.
Read the full post here.