Fusion with 2 Virtual Processors on MacMini

I'm running Vista Ultimate in Fusion on a 2.0GHz Dual Core MacMini with 2GB of memory. I have the memory in Fusion set to the default 1 GB. I tried enabling the two virtual processors for a boost to Vista performance at an expense to the Mac side of things. But Vista actually took a hit in performance (highlighting and opening folders lags a bit, boot time increased, launching programs increased).

Is the 2.0GHz Dual core processor being taxed too much to run the two virtual cpus in the Vista VM?

I've read about others getting a performance boost when enabling the two virtual cpus but they were using iMacs and Mac Pros. Thanks in advance for any advice.