What I mean is I want my selected 2GB of music to be on the iPod
It might be worth using Manually Manage Songs as Gerard already said.
Nope, got me wrong...that's what iTunes already does, it plays only the checked items.
Yep that's right...
What I mean is I want my selected 2GB of music to be on the iPod, but I want to listen to the whole library (12GB of my mp3s are in the iTunes library) when using the computer
If the songs are checked in that 12GB library they'll play. If they're unchecked then they won't play. So if you uncheck 6GB worth then that 6GB won't play - only the other 6GB which are supposedly checked will play. And it doesn't look like there's a way to change it either.
And according to CNet:
Uncheck songs in the iTunes Library, and they won't show up. (Unchecked songs do not play in iTunes by default. They play only when double-clicked.
I just did a test now and I unticked several songs and iTunes just went on by - it didn't see them. But if I do re-check them then they will play.
An iLounge.com article shows this:
You can create a playlist using subtraction:
Playlist "All Checked" is "length is greater than 0:00" match only checked songs.
Playlist "All Unchecked" is "Playlist is NOT All Checked" and DO NOT CHECK "Match only checked songs".
Then, to create playlists from the All Unchecked:
Playlist "Mad Polka" is Match ALL "Playlist is All Unchecked" "Genre is Polka" limit to 25 hours.
Close to what you mean, I think.