Please reread the above posts--the original poster was using a version with CentOS 4, presumably because he is using CentOS 4.
I was just pointing out that I was having the same issue with CentOS 5.1.
It appears both use the same samba version, but with different packages of course. My yum reports:
samba.i386 3.0.25b-1.el5_1.4 installed
Also, this might be a known issue with 3.0.25:https://bugzilla.samba.org/show_bug.cgi?id=4973