A description of the errors you get, as well as your configuration (machine/OS/version of Perl) would be helpful. As it is I can only guess that your machine might not turned on ;--)

On *nix, to install XML::DOM you need first to install the expat, then you can either use CPAN (or CPANPLUS) to install XML::DOM or just install XML::Parser then XML::DOM.

On windows use ppm, I believe Activestate's repository has a ppm for DOM.