Additional memory in iBook G4 causes wifi to drop out

I have a iBook G4 (1.2 Processor, OS X 10.3.9, purchased Feb 05). My computer comes with 256 built in and I had another 256 card in as well. I took out the 256 and put in a 762 so that I would have more memory and be able to install Leopard. As soon as I put in the new memory, the wifi started having problems. It works, but I have to be within six feet of the base station or there is no signal. Others seem to have similar issues (possibly from the heat? the memory is right under the airport card). I took the memory out last night and the internet is completely normal.

Has anyone else had this problem? I am getting a 512 card, so I will have 762. Will that be enough to install Leopard or should I just give up and stick with 10.3.9?

Thank you!
Mary