This is for Windows versions of the games. I don't know of any problems with freezing on the Mac versions.
The first thing to do if your Petz or Babyz game freezes -- say the bar freezes when you try to start up Petz 4, for instance -- is to remove all downloads, hexies and pets from your game's directories. Put them somewhere safe, of course. Now try loading the game. If it still has the problem, reboot your computer and then hold down Ctrl + Shift while you restart your game. This should re-set your Registry entries for the game and let it run with no problems. If this works for you, then you can put back your hexies and pets. It's often best to put them back a few at a time, loading the game after putting back each batch to check that none of them contains a problem file.
If the Ctrl + Shift trick doesn't work, then you have probably got some stuff in the Registry that's not getting re-set and/or some keys that have become corrupted (Omar's Debugger writes extra stuff in there, and the game's re-set mechanism won't necessarily remove it). In that case you need to remove the entries manually. Don't panic, it's a simple procedure:
At the start button of your computer, choose Run. Type in Regedit.exe. This will open up the registry so that you can edit it. Editing the Registry can be dangerous if you don't know what you're doing, but I believe that modern machines have a Rollback system and anyway, you're not going to do anything terrible here.
Now, navigate by clicking on the little crosses in the left-hand pane. I'm assuming it's Petz 5 you're working with, so click on the one next to HKEY_LOCAL_MACHINE. Click beside SOFTWARE. Click beside StudioMythos. Click beside Petz 5. Now you've run out of little crosses, so click on the folder 4.00.00. What you see in there is all the stuff that Petz 5 writes into the registry each time it's run.
(just in case anyone else tries it with Petz 3 or 4 and is confused by my directions, after they get to the HKEY_LOCAL_MACHINE and SOFTWARE, what they should be looking for instead of StudioMythos is "PF Magic" (without "" quotes of course) and then either Petz 3 then 3.00.01 or Petz 4 then 4.00.00. And if you're dealing with Petz II or Babyz, their keys are both under PF Magic also of course.)
Now, from the main menu choose "export registry file". This will do absolutely no harm; it's a safety measure in case you want to get back to where you were. Export the file to somewhere that you can find it again on your hard drive if you need to.
Right. Now I want you to _delete_ that key in Regedit. It will do no harm to your machine, and it's the most complete way I know of to re-set your game's registry settings.
Okay, close Regedit. Reboot your machine. Now go to your game's Resource\keys directory using either Windows explorer or My Computer, and move all the keys out of there to the same temporary place where you put the exported registry key.
Now start the game. Your problem will, I hope, be solved...
For people who have later operating systems than mine, which is Windows 95, Miranda has this useful tip about backing up your Registry. Thanks, Miranda! Basically, if you have Scanreg on your machine, use it before you start fooling with Regedit:
"Okay, I read your Stuck Debugger thing and I was reminded by it about this neat thing; I don't know if you have it in Windows 95, but in my C:/Windows directory there are two (registry) files: One is RegEdit, which, the first time you use it, warns you NOT to play around with your registry. The other is, I guess, in case you messed up with the registry. It is called Scanreg. If you double click on that last one, it comes up with a message saying that the Windows Registry has been scanned, checked for errors, and backed up."