Before you begin
The Gigabyte M57SLI-S4 seems to exist in at least 2 versions: one with a PLCC socket for the BIOS chip (socketed BIOS), and one with the PLCC BIOS chip soldered onto the board (soldered BIOS). The former might be a pre-production board since nobody has so far (2007/03) confirmed the purchase of a M57SLI-S4 board with socketed BIOS.
The fact that the BIOS is soldered onto the board complicates matters considerably, because it means that one flash of a faulty BIOS will 'brick' your board.
It is possible to desolder the BIOS chip, and replace it with a PLCC socket. You will need some good tools (heat gun/pencil, good soldering iron, etc) and soldering experience to do that. There has also been some speculation about the paths that are visible on the board for a second PLCC chip, and whether it would be possible to put a PLCC socket on there and switch between the on-board BIOS and the socketed BIOS.
If you're going to work on this board, I suggest you put a socket on it, or ask a friend to do so. It's just too risky otherwise.
Once you put a socket on the board, you will also discover that the RD1-PMC4 BiosSavior does not work with this motherboard: the RD1's built-in chip seems to be incompatible with the mainboard. This means you will need to hot-swap BIOS chips until you have a working LinuxBIOS chip. Plugging your BIOS chip into the RD1 and switching it to 'ORG' does work though. I have used the BiosSavior to ease hot swapping; it's a lot easier to pull out the BiosSavior and replace the chip plugged into it than to replace the ROM chip on the board.
Finding a BiosSavior can be a little tricky - most resellers seem to be out of stock, and the rumor is that IOSS has stopped producing them. This is the list of resellers:
I was able to purchase a couple (2007/03) from Eksitdata in Sweden.
This wiki page is maintained by Ward Vandewege (ward at gnu dot org).