This is a major FAQ at work so I put together some instructions. Hope this helps! (Hint: The Mac's IR port can sometimes be active so Steps 12 and 13 MUST be in that order or the Palm thinks it's receiving a beam.)
1. On your Mac, launch HotSync Manager.
2. Select "Enabled" in the HotSync Controls tab.
3. Click on the Serial Port Settings tab.
4. Under "Check for handheld connection using:" choose "Local Setup".
5. Under "Local Setup - Port:" choose "Infrared Port" from the pop-up menu.
6. Quit HotSync Manager.
7. Turn on your Palm.
8. Tap the Applications button.
9. Tap HotSync.
10. Select "Local"
11. Tap the pick list and choose "IR to a PC/Handheld".
12. Tap the HotSync Icon.
13. Align the Palm with the IR port of the computer.