There was a lot of discussion on the iPodLounge.com forums regarding this issue the last time the iPods were updated.
It seems that every person is told a different story by their local CompUSA. Some people were told they were simply allowed to "trade-up" by paying the difference between their model and the new one, while others were given a factory refurbished 5GB in exchange for their broken 5GB, even when the 10GB was going for the same price the customer paid for their original 5GB...
Give your local CompUSA a call and let us know what you find out!
-Josh
PS-I sent my 20GB in to Apple for repair last week. The status says "Replacement Ordered"...I am hoping that since the 20GB is no longer around, they'll send me a new 30GB, but the woman I spoke with said they're just sending a factory refurbed 20GB (which isn't fair, considering I purchased a NEW iPod, not a refurb)...