packages kept back

i am running ispconfig on ubuntu 8.04.
when i run the apt-get update and upgrade commands, i am told that the following packages have been kept back and then it list the five packages.
Here's my question, why are some packages not being upgraded? Is there a way to fix it and do I wanna fix it?
AcidKat

 

linux-image-server linux-server openssh-client openssh-server ssl-cert

 

This link might help: http://www.debian-administration.org/articles/69

 

will this break my server?

 

i did what you said and it is running fine
thax a million guys
AcidKat