You have 2 options:
"PocketMac" (
www.pocketmac.net) and "Missing Sync" (
www.markspace.com).
Pocket Mac supports Entourage but is less "refined", missing sync is a cleaner app but only syncs addressbook and ical. Both work with bluetooth. If your mac doesn't have bluetooth buy the D-Link usb bluetooth adapter from the apple store (it works on the passive usb port on your keyboard).
All together we're talking about a EUR 80,00 investment.
If you find any other options please post them here.
Kermit
iPaq 5550 + bluetooth GPS
Nokia 6230
Apple G4 Desktop
HP NX7000 laptop