As one of the other responders mentioned, you should look at the Domino Everyplace products ... and in particular look at the new beta for Domino Everyplace 3.0, Beta 2.
It directly supports access to mail, calendar, etc., for the iPAQ's Pocket Internet Expolorer.
Start here:
http://www.lotus.com/rw/beta/dz522qhh.nsf/keywords/WelcomePage
Be aware that DE 3.0 right now is NOT a sync product ... it's strictly for realtime, rightnow access.
If you're looking to sync to the iPAQ, then Cadenza (www.commontime.com) or Pylon (www.avantgo.com) are more appropriate. Cadenza works against R6 right now, as does DE 3.0.
- Rob