In my previous post, Generating heavy loads using Visual Studio Team System for Testers 2005, I explained how the the GC configuration can be changed for generating heavy loads on Multi-proc machines.
For Visual Studio Team Suit 2008 for Testers , there is a change. VSTestHost.exe is now hardcoded to use only one CPU. Which means, even if you change the GC settings in the config file, it will be overridden with hardcoded Workstation GC settings.
To generate heavy loads using VSTT 2008, you have to use the Agent/Controller setup. Once the Agent/Controler has been configured, change the Server GC settings in QTAgent.exe.config on the Agent machine and you will be good to go.