Yes, and you have several options:
1) Both users share the same (Windows or Mac) login account, and thus the same iTunes Library.
For this option, the auto sync feature must be turned off for both participating iPods, but may be the wiser method if both users have similar tastes. To do this in iTunes (Mac or Windows), mount one iPod and click on the iPod Preferences button in the lower right corner of the window, then select either ‘Automatically update selected plyalists only’ or ‘Manually manage songs and playlists.’ This will deselect ‘Automatically update all songs and playlists’ so you can now sync to multiple iPods. Now, you must either manually load each iPod, or automatically sync to only a select number of playlists.
2) Users each have a distinct (Windows or Mac) login account, and thus do not share an iTunes library.
When multiple users on a computer, each with their own iPod, each have their own login account, their iTunes libraries are completely distinct. In this situation, the iPods can automatically sync their entire respective libraries (as is the default setting). However, if both users have similar tastes in music, they may find unnecessary desktop hard drive space being wasted, as each distinct iTunes library will have separate copies of identical songs.
Choose the method that suits your situation best.