You'll need accessory hardware.
AFAIK, none is available for the 5G iPod (with video) yet. I'm waiting for some to appear - 44.1 kHz recording ability was one of my justifications for getting a new iPod.
iPods have been able to record since the third generation (the ones with the four buttons up above the scroll wheel), but only in 22 kHz mono. They've always required some sort of accessory like the iTalk et al.