Fast XP-VM-Setup?

I have:

• a Windows 7 Ultimate x86 (32bit) machine which runs vmware Workstation 7.x
• it has 4Gb Ram and an AMD Phenom x4 695BE CPU (4x 3.4Ghz)
• 10 Windows XP Pro keys
• an original Windows XP CD x86 (32bit) Professional with SP3
• and an iso Image made from this CD

I'm planning to run a computergame in a VM. Official reuireements are:

• Microsoft Visual C++ 2005 Redistributable Package
• Microsoft .NET Framework 3.5
• Microsoft DirectX 9.0c
• 2 GHz CPU
• 1Gb RAM (tested with [512Mb Ram]+[1Gb virtual RAM]
• GPU: [nvidia: GeForce 5 or better] or [ati: any 9xxx after]
           Shader Model 2.0
• GRAM: 512mb

I already made a normal xp VM and gave it 512Mb Ram+1 CPU core. I set it to be optimized for performance:

http://law.wustl.edu/computersupport/help/Instructions/Optimize%20WinXP/How%20to%20optimize%20Windows%20XP%20for%20the%2…

I cloned it 4 times (linked clone).

With 3 VMs it works pretty good. 4 VMs results in chaos: nothing works correctly, everything slows down as hell...

So what do you suggest me to do to get more than 3 vms running at the same time?

Should I download Micro-XP or some another custom Image? Or should I make one myself using nLite or w/e? (How long would I need to do that?)

Or should I just use my original XP CD and tune it up a little?

I really hope you can help me.

best regards,

PheeL