Xbox hard drives are locked to the specific motherboard. In order to switch a drive between two, you would need to extract the key from both xboxen and then unlock the donor drive and re-lock it with the new key.
At this point, I would take the extra effort to clone the donor drive's data onto a larger HDD (Because I assume you only want it for the gamesaves/songs) and lock the larger drive. I found a 120g drive on newegg for like $10 that worked well. I'm not sure if there are still any available. I'll edit this in a minute to tell you.
There aren't any available, but this is a pretty good link to click from time to time if you want an idea of options:http://www.newegg.com/Product/ProductLi ... 359%3A7788
Go here, read stickies:http://forums.xbox-scene.com/index.php?showforum=41
Particularly this one:http://forums.xbox-scene.com/index.php?showtopic=659887
Geb's a wild and crazy dude. I can tell, only the most adventurous people keep the hotsauce next to the deodorant.