Vista - Windows Server 2003 vs. 2008 - very different speed of work

Hello!

I have host comp.(3GHz CPU, 2Gb RAM, WinXPprofSP2) with two VPC: one with
Windows Server 2003(WS2003) and one Windows Server 2008(WS2008). Both VPCs
configured almost identically and both WS setting to conserve resource: all
graphical features are off, all visual effects are off, font smooth off an so
on. At any point of time only ONE VPC can work, I never start both VPC
together, since I allocate for each VPC 1.2Gb of memory and total volume of
memory=2Gb. So - I work with WS2003 OR with WS2008.
The problem: WS2003 work really fast, it's very close to normal "hard"
computer, but WS2008 is horribly slow. Example: right click to desktop to
show ordinary menu. WS2003 show menu almost instantly, WS2008 show it more
then 3(!!!) sec. after click. The dialog "System"(with computer name, CPU
speed, etc.) in WS2008 opening up to 10(!!!) sec. ((
What I can do and how to tune VPC/WS2008 itself to resolve this "speed
problem"?

I thank in advance for your answers!