How to edit files in a Linux vmdk

I am trying to edit a couple config files in a Linux vmdk.

I am using the Disk-Mount utility (ver 5.1.0) from within a Linux host running CentOS 2.6 - 64 bit.

(The vmdk I am trying to edit is not part of this host)

I can mount the vmdk and see all the files, but if I try to edit, I am told it is a read-only filesystem.

If I run the mount command - it looks as if the filesystem is rw.

Any help would be appreciated.

Thanks.