I've heard that OCZ DDR2-667 PC2-5400 doesn't work nicely with Gigabyte GA-965P-S3 mobo until later BIOS revisions. My question is, if the ram doesn't work will the computer not boot at all, or will I be able to install the latest BIOS with a floppy and then go from there?
Have you tried the RAM or are you thinking about getting it? If you're thinking af buying it, personally I wouldn't. Better off getting memory you know is compatible. Most mobo have a chart of compatible RAM
The only way to find out is to put the machine together and see what happens. I'm guessing you'll be able to up date the BIOS. If it were me and the machine starts up and you can into the BIOS, I'd try to install Windows and then do the BIOS update. You may not have any trouble at all. Best to deal with problems when they arise rather than anticipate them, definitely helps your sanity.