I don't know about the iCal syncing but I'll comment on your other questions...
Your machines will see each other. You can enable filesharing over your wireless connection. It works in exactly the same way as a wired connection in this regard.
If your Pismo has a 100Mbps ethernet port, use a wired connection (all you need is a regular ethernet cable...the PowerMac, like all modern Macs, autosenses whether it is connected to network hardware or directly to another machine and compensates accordingly...) since it will be much faster than the 11Mbps Airport link.
Either way, I would use Carracho (
www.carracho.com) to transfer the files since it is more fully featured and markedly faster than AppleShare.
If you haven't properly secured your wireless network, you are potentially exposing yourself every time you use it. See this thread
http://forums.macnn.com/showthread.p...hreadid=142372 for more info.
Peter