Hi,
Can I copy a downloaded rom to a floppy and use with my A500?
Nope
The Amiga 500, like all Amiga`s except the A1000 has the rom...ermmm in a rom... Its a chip thats mounted on the motherboard.
Also a rom downloaded off the net is illegal, Amiga have never given the right for anyone to upload the rom image to a web page.
The only way you will be able to upgrade your Amiga is to buy the kickstart chip from an Amiga dealer (Yes, All Amiga stockists will carry the kickstart for your Amiga 500) and if the rom was a real 100% correct dump of the original kickstart you would have to buy an Emprom burner and make the chip yourself which would cost a lot more than the legal chip.
Sorry.