Well, I have only edited a couple of DSDT's, but there's a search function, there's a template and it's pretty much a matter of copy/paste change a couple of lines and you're done.
IBOOT? I used the really old boot CD as the new ones played up for me, but that's not important. Yes, I used the Multibeast the last time around for the kexts and DSDT, but I've replaced much of that by now and Tonymac kindly made a new DSDT for my board based on the F7 BIOS. But the plain DSDT's don't have the right graphics information in them, although in your case it might have the details for a 9400GT rather than an 8400GS as you'll need.