Over @ ipodmods.com, they discovered that a 40GB Toshiba drive will also fit in place of the 30GB drive.
We have found that the Zune battery is the same as the iPod Video 60/80GB battery. We can start upgrades for existing Zune customers now. We have also found that the new ZIF drives from Toshiba will work in the Zune players. You will be able to upgrade your 30GB Zune to a 40GB right away. We have not found a way to insert the 60GB or 80GB drives yet, as the back panel would not fit back on if we did this.
Read the post @ ipodmods.com here