NIS - FreeBSD server and Linux clients

[Tom Munro Glass]

I want to use my FreeBSD 4.9 server for authenticating logons to my Gentoo 
clients. I've set up NIS server as described in the handbook, and if I run 
ypcat on the Linux client, it is obtaining information from the server. 
However, it is faiing to authenticate users defined on the FreeBSD machine. 

Should this work, or is there a problem with the differences between how 
FreeBSD/Linux use the passwd file?

Any advice would be much appreciated.

Tom