Once you have installed winamp all you need to do is download the plugin from the site above and install it. If you want to scrobble to last.fm you need to check the box during the install as this feature is not installed by default.
Once it is installed, connect up your ipod (it supports most ipods) and it will ask you for some details about what model of ipod it is. You will also need to enter your last.fm details into the “Audioscrobbler for Winamp” plugin (found under General purpose plug-ins).
You can then sync your ipod with your winamp library. Each time you sync it will update the playcounts (both ways) and submit any newly played tracks to last.fm. As with any other method of scrobbling you need to make sure you sync before playing any tracks in winamp, otherwise any previously played tracks will not be accepted by last.fm
There is very little configuration required for the ml_ipod plugin although there are a lot of options that you can explore.