MacOS – upgrade MacOS X 10.4 to 10.7 Lion

If you are in the US or Canada, you can call 1-800-MY-APPLE to order Snow Leopard directly from Apple telesales. It should only be $20, a discount from the original $30 price.

This will only work if you have an Intel Mac, of course.

Do you have specific files you are transferring? Ie, your home account? If you put the old Mac into TARGET mode, you can use the ThunderBolt->FW800 adapter and a FW800->FW400 cable to mount your old Mac like an external drive and copy whatever you need over. The migration assistant may be able to read from the drive to pull data as well.