I have an imac: 10.4.11 2.8 ghz
If it is running Mac OS X 10.4.11 "Tiger" and has a 2.8 GHz CPU yours is most likely an iMac7,1: 24 inch screen, from 2007.
If that is true it will certainly support WPA2 Personal. Though upgrading your Tiger iMac to Snow Leopard is certainly a good idea, that alone is not likely to solve the problem. Something else is going on.
Ask in the Mac OS X v10.4 Tiger forum if Tiger specifically supports WPA2 Personal or if there are any problems with it on your iMac. I am only 99% certain it will work, but if anyone is 100% certain BDAqua will be one of them.