The Archos AV700 7" has a 100gb hard drive. It also has a 7" widescreen screen, which is a bit of overkill for what you want.
Don't take this as gospel but I'm pretty sure the Creative Nomad used a 2.5" laptop HD. If you can get that (ebay is your friend) and a suitable HD then that could work.
I can't remember where but I saw a tutorial on replacing the 1.8" Creative ZEN Touch HD. I remember it being a bit more difficult to do though.
P.S. If you decide to undertake these mods please be aware that you do so at your own risk and I am in no way responsible for anything that goes wrong.