A lot of others are asking for the same thing:
http://www.google.com/support/forum/p/Calendar/thread?tid=6950872dc50541b6&hl=en
Please let users choose a calendar for the Google Calendar / Outlook sync function. Right now it just syncs with the main calendar.
Listen Google, 99.9972% of businesses use Outlook. Deal with it. People want to sync their work with their personal calendar using Google Calendar, but maintain them separately. So howsaboutit?