Q: Can I use the USB power adapter that came with my (4G) 60G color/photo iPod to charge my newly-purchased (5G) 80G video iPod?
A: Absolutely. All of the iPod power adapters that use the Dock Connector are compatible between the different generations.
The only small exception to this is with regards to the third-generation (3G) iPod. Adapters built for the 3G will work fine with any other model, but since the 3G only charged via FireWire power, as opposed to USB, newer chargers may not work with an older 3G iPod.
Every model after the 3G that uses the Dock Connector, however, including the iPod mini and the iPod nano, will charge over either USB or FireWire, so other than the exception for the 3G noted above, you can charge any model of iPod with a Dock Connector using charging accessories built for any generation of iPod.