cannot remove gdm

[Tran Tuan Anh <trantuan@comp.nus.edu.sg>]

Hi all:

here is the error I got:

"Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.

Since you only requested a single operation it is extremely likely that
the package is simply not installable and a bug report against
that package should be filed.
The following information may help to resolve the situation:

Sorry, but the following packages have unmet dependencies:
  kde: Depends: kdm but it is not going to be installed or
                x-display-manager
E: Sorry, broken packages
"

I really want to remove gdm out..
Could anyone tell me how to deal with this?

Many thanks!
Tuan Anh