1st and maybe 2nd gen sync and charge only over firewire and need a hard drive. I tried a comact flash and a zif ssd in the format of the newer hard drives and it finds the drive, but wont format. It stops half way. The newer ipods (3rd gen and up) that sync over usb can use solid state alternatives (2nd gen is the same ipod with a bigger drive and a touch scroll wheel). If you can find a zif ssd smaller than 32gb it might work, but dont forget about the zif to 50 pin adapter.
ZIF SSD KingSpec ZF18-32