Found this little ditty from on10.net who in turn pulled it from Peter Provost
In Windows Vista, there’s a setting that lets you configure your PC to use both cores upon booting up (by default, it only uses one). You can change this setting in the System Configuration menu to get your PC to boot faster. Here’s how:
1. Go to Start, type msconfig and hit [Enter]
2. In the System Configuration Window, select the Boot tab
3. Click on Advanced Options
4. In the BOOT Advanced Options dialog, check the "Number of processors" check box, and choose 2 (or 4 if you have quad core) for the number of processors.
5. Click OK twice