Seagate external hard drive works on some computers and not others

I have a 1T Seagate external HD. I upgraded to the new Snow Lepard recently and ever since then I can't access it. There are a ton of posts about this, I know. But when I plug it into my friends Imac, it runs fine. But when I plug it into my MacBook, it says "This device cannot be read by this machine" and asks for me to ignore or eject. I have no permissions. I can't mount or unmount, delete or partition. On the Imac I have all the permissions though. I have changed all the settings to make sure that everyone can read/write. But the laptop still can't use it. I have Iphoto from a few of my friends computer's backed up on it and that doesn't allow you copy it so just erasing or reformatting is out of the question. Any ideas or help would be awesome!