Depends what 233MHz PPC Mac this is-- I'd take a guess at a Beige G3.
The key is to find out if the Beige G3 is PCI 2.1 compatible; if so -- you are in business. I don't know this off hand.
There are a number of good options, the main one is ensuring you get a PCI card with the Broadcom chipset as this will be seen as an Airport Extreme card.
An example is the Belkin F5D7000 Rev. 1 and 2 like I have in my PowerMac G4; it is seen and treated in every way as an Airport Extreme card and cost much less.
These pages may help you:
http://homepage.mac.com/techedgeezine/2005_0217-54g-inyourmac3.htm
As I say the key is knowing whether these Beige G3s (if that is what this is, if not it may be a 604 based PowerMac) support PCI 2.1. If it doesn't, maybe a USB PCI card with a USB WiFi dongle.
Supported USB dongles are the DWL-122 from DLink and any such adapter with the Prism wireless chipset such as the Netgear MA111 rev. 1 -- these drivers are found on DLink's website. Also RALink based wifi dongles are compatible with the drivers on their website.
Vicky