Try setting them both to cable select, but keep them in the same order (80gb W.D. at the end of the cable, Seagate in the middle) this way the bios will automaticaly set them as primary /secondary and will choose the correct mode to run them in, this all depends on the age of your mobo, older motherboards sometimes have problems recognizing newer bigger H.D.'s, if thats the case I think abios flash is your only option (dont quote me on that though) in that case take it to a pro, let them bear the consequences of making a mistake, and I'm sure was a given but what kind of IDE cables are you runnig, make sure they are 80-pin and depending on the specs for the seagate, might want to think about getting ATA 100/133's there only a couple dollars, either way FAT\NTFS is not your problem, I'm 99% sure you cant run them both at the same time ( you have set them up on a dual boot) for example my computer has a recovery partition at the end that is FAT and I cant get into it unless i want to run recovery, in which case I have to start from scratch, My friend has a copy of WIN 98 on a seperate HD for gaming (win 98 has to run fat) and has to reboot if he wants in, i;m sure thats not what you want, post the specs for the computer and the new drive and I'll have a better idea