I am hoping to buy a 1.5TB external usb hard drive. I am going to use PSGROOVE on my ps3 and ive also got a softmodded wii. Will it be possible to load both PS3 AND Wii games onto the external drive so all i need to do is swap the usb cable over to each console when im playing?

At the very least, they can't be stored on the same partition because the Wii uses a proprietary file system. I'm not sure how each system handles multiple partitions (assuming they handle them at all).