I'm supposed to use DDR2 5300 (667MHz) RAM for my MacBookPro 4,2. The max is 6GB, and I already have 4GB (2 x 2GB), so I only need a single stick of 4GB. So far it looks like this spec RAM runs about $100.
4GB of DDR3 RAM runs about $20.
What are the consequences if I put the wrong RAM in? Will it work at all? Will it damage the RAM or the computer?