and how do i find which atmega has the right bootloader for my arduino duemilanove board???
Bare ATMega microcontrollers don't come with a bootloader by default; the bootloader, if there is one, is either put on by yourself, or if you are buying pre-bootloaded ATMegas, it was put on by someone else in the supply chain. Hopefully, if you are buying such a pre-bootloaded chip, the person/company you are buying it from can tell you which bootloader they put on it.
Regardless, though, if in doubt, flash your own! Note that this may require experience and tools you may not have; since you are asking these questions, I can almost say for certain that you lack both, so you should stick (for the time being) with pre-bootloaded chips, and talk to your vendor.
