I'm confused about a few things.

I host a site with 1 company and have the nameservers with them for the domain.
My customer now wants to use this 'message hub' service and use sync email utilities for the business.

They have told him he needs to change his nameservers over to them, however we will lose the website if he does this. iS it possible that you can have emails with one server and website with another??

1 way around the problem would be to use web forwarding, but this will use frames to do it.

what options will i have?
Also on a side note, what is the difference between DNS and nameservers?