I also agree with them and upgrade it to at least 256MB of RAM (They use SODIMMS) and put Mac OS X.3 (Panther) on it with all of the updates. You can't get a fell of Apple's products if your using 1999 technology. Panther will actually run pretty well on that iMac if you have at least 256MB of RAM. Now, its not going to be a speed demon and won't run things like iDVD, or GarageBand, but you can easily run Microsoft Office 2004 for OS X, Safari, QuickTime, etc...
When you get that up and running, try looking at the D-Link USB Wireless adapter. Its not bad though the software for it is a little shaky. I found that after I repaired the permissions after installing the software for it then OS X was much stabler. Please don't blame Apple on stupid developers who make crappy software/drivers for their own products which makes the OS unstable. Apple has no control over that. If you have stability problems then the first thing you do is repair permissions! After you install the drivers and plug it in, go to the Network System Preferences and it should eventually detect it and install the USB Wireless adapter. It should say something like en02 adapter when its detected. If you have any other problems please write back...Mac people are always willing to help!
BTW...I'd look on eBay to get that D-Link DW122 wireless adapter. Make sure its the model DW122 or else it won't work on a Mac, specifically in OS X. They usually sell for around $30 + shipping on eBay, which is a heck of a lot cheaper than buying it brand new.