Depends on the power of the iBook. How many Mhz is it? 800Mhz and higher would be fine. But that might be around the time Apple updated the iBooks to G4s. I can't remember.
I'm running Panther, slowly, on an unsupported 233Mhz Wallstreet Powerbook. Must say I appreciate having a dual cpu tower. Someone mentioned one of the last G3 PBs. That might be OK at 500Mhz, but I'd try before i would buy. The last one (Pismo) came with both Firewire and USB.
Do some price researching and watch the Apple refurb page for the occasional decent deal. Ebay is good to watch.
I'm with Abdiel on this. If you can save some extra money, you'll be able to get a beefier system that will make the experience more enjoyable. For instance you'll likely want at least 512MB of ram.
As for the wireless cards. You definitely what to go with an Apple solution. That means the PB you buy needs an internal slot for the Apple branded card which only came as an internal option. No third party card/software solution allows for the highest encryption (WPA), as far as I've been able to find out so far.
There have been two wireless cards from Apple and you can only use one of them for which ever PB you buy. The first version, no longer sold, was a 10Mbit card while the newer one currenly being sold is 54Mbit one.
The other thing to consider is the software you'll be running. Video chatting takes at least 600Mhz, officially. Editing video or Garage Band files takes alot of horsepower too.
Personnally, if you don't really need the portability of a laptop, consider a Mac mini. And for that I'd consider waiting for version 2. Hopefully that will be out within a couple of months. But only Apple really knows that.
Good luck.