Server unavailable thanks to DHCP duplicate name

I work at a college where are servers have names that are just a little to common. Yesterday a visitor came on campus with a mobile device we shall say was named "Sam." Coincidentally , "Sam" is the name of our Windows print server.

Once the mobile device got registered in DHCP, lo and behold... no one could print. According to our network expert, deleting the mobile device "Sam" from DHCP resolved the issue. Of course, we're on pins and needles hoping that the visitor has left for good.

But my real question is this: what is so messed up about our network that this could happen at all? There has to be a way to prevent this from happening again. Put all our servers on their own VLAN is the first thing that came to my mind, but I'm not a VLAN expert. I don't know what the implications of that move would be.