Short answer: No.
Less short answer: Not now.
Apple's .Mac iCal system is purely for viewing one calendar at a time over the web. iCal publishes a vCalendar file (an open standard) to the .Mac website. Apple's web calendar reads that file. If you were to make changes online, they would be overwritten the next time you made a change in iCal itself.
I'm working on a similar web-based calendar viewing system, and I considered allowing editing, but I have no way to save information back to the iCal app. If you subscribe to a calendar you are also publishing, you get overlapping duplicates. (I just tried it. Crazy.) That kind of editing would require a syncronization system of some kind.
Which brings me to your second question: can you sync iCal with a PocketPC or iPaq? Not yet...but I'm almost positive that will be one of the many applications of iSync (
http://www.apple.com/isync/).