I've just had my first run through make it into ToB. I still have a couple other games in SoA.

However, when i tried before to load ToB from the start (just to look around) it gave me a message that i wouldn't be able to access SoA from that point on.

Is this true?

Or is it just true for the specific game that i would have (imported?) played new?

I don't want to lose access to my unfinished SoA games, yet, i want to play ToB.

any thoughts?

Thanks!

You can simply go back to your SoA game by loading one of your SoA saves. The message that you got was saying that the party that you just took into ToB could not return to SoA. So just open up SoA and load your game where you last were

Throne of Bhaal is a new part of the game, which adds the Watcher's Keep to Shadows of Amn (so when you have Throne of Bhaal installed, and you're still playing Shadows of Amn, you can access the Watcher's Keep), AND ToB. That's the only part of Throne of Bhaal that truly affects SoA.