Thank you all for your helpful advice. I knew I came to the right place.
I finally got word back from LaCie. They said that since mine is an internal IDE drive, there is no problem with using firmware from NEC as opposed to from LaCie. For those of you with firewire or usb connections, beware: LaCie rewrites the NEC factory firmware to use the different connections, so don't use firmware directly from NEC.
Technically, NEC firmware could void the warranty, since the drive is branded by LaCie and warranted by them. But LaCie gave me in writing that it would be fine, so I'm good.
And as far as voiding warranties...well, I'd probably be agreeing with thousands of others on this site when I sarcastically say, "what warranty?"
The gains from a well-tested firmware hack far outweigh the risk on a drive that only cost $60.