We can try this and see if it will work.
Your iMac takes an SO-Dimm memory module. There is only 256MB on board, but it is very hard to get to.
So, we have to try and get as much memory in that SO-Dimm slot that you know is empty.
The logical size for that slot would be 512 MB making the total 768MB.
for some pricing on ram SO-Dimms.
That takes care of the memory. As far as the Tiger 10.4 OS X upgrade, that's gonna cost you a little more. Actually a lot more.
The cheapest I can come up with, that is at least guaranteed (unlike the sellers on ebay for example) is at Amazon.com.Tiger retail install on DVD
. You MUST have a DVD drive or a COMBO drive that reads DVDs to install this OS X package.
That will take care of getting Tiger/10.4 in the Mac. Then run Software Update from the Apple Menu and let it install the update to 10.4.11 for compatibility with the AirCard you want.
Hope this helps,