Exactly, I guess you could do the same with smbmount and samba but NFS is more of a native unix/linux thing and has better user control/interoperability.
Either way if you aren't worried about the security issues you could "share" root / on one box and mount it into say /otherroot on the other machine and vice versa. FYI this is considered very insecure although where I used to work we had many windows users and few people who knew any unix/linux so our whole dept. shared all our boxes' root dirs with NFS under Solaris Unix
And NFS is fairly simple as I remember it, check out man nfs and man exports for basic info and theres an NFS-HOWTO (sorry, it's been awhile since I have used NFS or Solaris so I'm way rusty though I need to set it up again soon.)
In Slack you should notice that it tries to mount NFS shares on boot already (from /etc/rc.d/rc.inet2 if it's not #'d out) so it's probably as simple as defining shares (that's in /etc/exports), adding connections to them (on the other box's /etc/fstab) and then mounting them.