When you moved you stuff to the external you could still see your tracks in iTunes, right?
And they all played, right?
All your playlists should still be intact, are they?
If the answer is Yes, then when you connect your iPod to your computer, iTunes will sync as normal because iTunes knows exactly where the original tracks are.
Before connecting your iPod, make sure that all your music and stuff is still playable from within iTunes and that there are no warning icons next to any tracks.
If there are warning icons, click the track and "find" the missing media, it's probably on your external.
Once you are satisfied that everything still plays, go ahead and connect the iPod.
Personally I prefer to have iTuns NOT automatically sync my tracks. I have mine set to sync manually.
Good luck
P
I followed an excellent review on this site yesterday on transferring my iTunes library to an external hard drive. I had total success - everything went across safely and I deleted all the files off my C drive - and I downloaded some more stuff from the iTunes store onto my computer. But then, I suddenly thought 'what happens when I try to synchronise my iPod? Will all the music etc that's currently on it be deleted (there was a message that came up when I was deleting the C drive files that said they would be wiped off my iPod as well)?'
I'm a total wuss when it comes to technology and, quite frankly, I'm too scared to do anything! Can someone please tell me if there's a way to stop my iPod emptying when I try to update it with the new stuff or if it will automatically synchronise with the files on the external hard drive, as long as I have it plugged in when I attempt synchronisation?
Thanks very much in anticipation of your help.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic