Whether they will swap it is anyone's guess. I would definitely call Dell and explain your problem. SOMETIMES they can be very understanding. Other times no.
Did they get it direct from Dell or one of their distributors?
They should have had Office 2007 on that machine, but I personally don't like that one. I prefer Office 2003.
I have a laptop with Vista and am not disgusted with it yet. Some things I like, others I don't.
Good luck with Dell. Be kind and speak softly and don't make demands. They don't like it when people are too pushy, y'know.