There are probably a few ways to accomplish what you want.
- Online Calendars that sync with your Treo.
- Network Hotsync - this would require your Treo to be able to access the computer that has the hotsync and Outlook software installed.
- 3rd party Outlook syncing solution
- Seven
- Sproqit
- Carrier specific, such as Sprint's Business Connection or Verizon's Wireless Sync