At my office, we use Netscape for email and Oracle Corporate Time for Calendering. I do use Outlook as my IMAP client and use Oracles Connector to sync my Oracle calendar to Outlook. I do not have any issues in setting this up and my Axim sync's very well.
As for ActiveSync setting up network connection, this is done because Microsoft has decided that the device will communicate to your PC via TCP/IP. If you check your network connections you will see that an IP address has been assigned to Local Connection #2. (May only be visible when the PPC is plugged in). The issue in doing it this way is firewalls and network optimizer software seem to affect ActiveSync's ability to communicate with the device. If you use firewall's, you have to open certain ports (found on microsoft's web pages
www.microsoft.com/mobile). This is the biggest cause of issues however if you use Network optimizer software which might compress network traffic for performance reasons, make sure you unbind it from Local Connection #2 (if that is the connection that gets created when you plug your device to your PC). A lot of people have disabled the optimizer software on there wireless network card or local connection #1 but that has no effect on the connection between your PC and PPC. You must disable the optimizer software on the active connection for your PC and PPC! I hope this helps!