iPodMods has published a helpful guide to cracking open your Zune case and Zune-Online took the next logical step — they propose stuffing a 40GB Toshiba ZIF drive in there. Apparently the 40GB model works in the Zune but the 60- and 80GB models will not, mostly due to size constraints.
Is it worth cracking the bugger open for an extra 40GB? Sure. We wholly support endangering your electronics for a wholly superfluous purpose.
Upgrade your Zune to 40 GB [Zune-Online]