I don't think you need 48-bit LBA for recognition of 135GB+ drives. I'm pretty sure my file server doesn't have it enabled (though it does have sp1) and the machine has several drives larger than 135GB. I did have to update drivers for the IDE controller card (promise Ultra100) and flash that card's BIOS to get the drive fully recognized.
That said, check the website for the raid controller. You might be able to, or need to, do a flash on the controller. If it's onboard, you might still be able to update somehow, if you'll even need to in the first place.
I say: "go for it and fix it if it doesn't run from the get-go."