No, you won't be expelled from the guilds if some of their paths cross, but you might have a hard time finishing quests. Especially the thieves guild is a club you wanna join right from the start. The first time i played Morrowind, i waited a little too long, and they wouldn't let me join them, because i had developed some skills that are not specific for stealthy characters. I know it sounds silly, but it really happened.
You CAN be expelled from guilds though, for several reasons. Of course you can't go around attacking other guildmembers, but the one time i got expelled, it was because i slept in someone else's bed. And i was Archmage of the Mages guild at that time, go figure.
Edit: Mel, every time you find a grand soulgem (i think it's what they're called, they are those round yellow gems), pick it up and keep it in your inventory. Later in the game, you'll run into opponents, who's soul will allow you to enchant clothing, armour and weapons with constant effect spells, very usefull. Of course you need a scroll or a spell in order to trap an opponent's soul after you've defeated him'.
[ 04-28-2004, 06:28 PM: Message edited by: johnny ]