So you found some r0mZ you want to put on cart, eh?
Most 5200 binaries playable on an emulator are 16k in size. These files are really two 8k images that occupy non-contiguous address spaces. The first half of the file occupies addresses 4000-5FFF, and the second occupies 8000-9FFF. This type of file can be put on any Parker Brothers 5200 cart with a minimum of hassle. And let's face it, there are better things to do with a dozen copies of Q*bert, Frogger, and Popeye than try to find them new homes.
Getting into a Parker Brothers cart can be tricky, since the edges of the shell are glued together. The easy way to get one open involves flexing the edge just enough that the brittle glue will break, but the plastic shell will not.
Now that you've ripped the shell open, yank the 2764 EPROMs (there may be only one, but there will always be space for two on the board) and reprogram each with half of the binary. Refit the chips to the board.
For other binaries, the easiest thing is to burn the 32k file into a 27256 EPROM, then attach it to a modified cart board from any of the following games:
Open the cart, remove the shielding and the chip (or chips). Throw these parts away. The lower chip space will be empty. The 27256 will go in the upper chip space. If you want to socket the chip for easy swapping, cut a hole in the front of the cart shell.
The board modification itself is pretty easy if you can make sense of this picture. The idea is to use the two chip enables to create a single enable and another address line (A14).
I've received reports from people of dubious sanity (hi Alan, Jeffrey) that a couple more changes may be necessary. If it doesn't work as presented, cut the trace on the back of the board between /CE (pin 20) and /OE (pin 22), then tie /OE to ground.
Before starting, have a good look at the binary file. Many cart dumps floating around were really half-assed, with huge chunks of repeated data. Lots of files that are 32k in size can be trimmed down to fit in the 2 x 8k version, and some of those don't even need the lower 8k of ROM. Others have code only in the upper 16k (Millipede, for instance), in which case you can get away with a 27128 instead of the 27256 and skip all the board modifications.
If you want a socketed EPROM that can be easily swapped, go with the 1 x 32k version. If you socket chips to the Parker Brothers board (and cut holes in the shell so they'll peek out), it will barely fit into the cart slot. The Atari board conversion does not have this problem.