WPA2???

It should automatically choose encryption method according to what it detects looking at the network.
If you set WPA2 authentication only or your access point, and leopard keep switching to WPA, that's strange, but this is not something you change on the client side.

Can you confirm ?

On which of your machines? Note your PB G4 likely doesn't support WPA2; it only supports WPA. I'd have to go check the exact model # but only the last generation or two of PowerBooks support WPA2.

Any PowerBook G4 with the AirPort Extreme card (or 802.11g built-in) supports WPA2.

Earlier PowerBook using the original 802.11b AirPort card do not support WPA2.

I have this problem as well. I manage a WPA2 Enterprise configuration at work, and a WPA2 Personal configuration at home, so I am perfectly aware of what my configuration should look like. My MacBook Pro connected to WPA2 networks just fine last week.

Now, all WPA2 networks show up in the Network preferences panel as their WPA equivalents, and I can no longer connect to those networks.

If I start Boot Camp, the system connects to those WPA2 networks with no problem, so this is not a hardware issue.

I've tried several things here and have had no success. I've tried deleting the Airport-related preferences files. That clears out the SSIDs and such, but if I re-add those SSIDs, the WPA2 option still will not stick. I'm really hoping for some feedback from Apple on this. While it's not widespread, it does seem to affect a fair number of people and essentially makes the laptop useless on a wireless network that has WPA2 security enabled.

I was talking to an Apple support representative (I have a bum iSight) who said he actually had the same issue on his personal system. He also said it's a well-known issue and that a patch should be issued soon. Obviously not official word, but it's promising.

I have the same issue. I've entered my network information into Leopard setting up the WPA2 of course. It will connect and stay connected (that is until whatever glitch that is in Leopard drops the connection and then refuses to reconnect). But even while connected with great signal strength and access to all network hardware and the Internet, System Preference will still seem to show the network as a WPA network instead of WPA2. Perhaps this is just a glitch as to what it SHOULD be displaying versus what it is ACTUALLY connected to. Thus far, no networking issues to report as to why it shows WPA when the network is actually WPA2. Revealing the password in preferences shows it is still using the WPA2 key I gave it. Nothing more than a "AI typo" - at least for now.

OK, I can now confirm what you have said about WPA2 Personal -- it is working but is displaying as the wrong type. I am skeptical of WPA2 Enterprise (which is much more complex.) I'll test that out on Monday. It seemed to have trouble with EAP-FAST but don't hold me to that.

Try this command to see the real status of your Airport connection

/System/Library/PrivateFrameworks/Apple80211.framework/Versions/A/Resources/airp ort -I