bought today NWN and started Hordes of Underdark as a wizard, I am now 'underground' on the main mission, but I have already all the magic levels and I can summon loads of creatures etc. Is this normal? how do I downgrade?

The player character in HotU starts at level 15, because he/she is the character of Shadows of the Undrentide.

Didn't you know that SoU is independent of the original campaign but that HotU is the sequel to SoU? Don't worry though the two storylines are not too tightly connected, and HotU is the best campaign to start with because it has important features that SoU lacked, like having two party members and better companion AI.

I knew nothing about this game.....I am trying all the expansion packs, this game is huge.

actually HOTU is very hard so I need MORE magic, not less....I am constantly dying....lol.....great adventure, very atmospheric, I teamed up with that Deekin guy. I didn't know this game was that good

The game also scales a bit. The higher level you are, the more and tougher opponents you face..