DNS name selection

I see in setting up this DNS server that I have to have a name such as AFP548.com but in my case I am setting this up internally and the DNS server will not be seen by the internet so can I use a name without the 3 letter extension at the end (.com, .net, and so on) ; such as; Macintosh.local.ID_macserver. Do you think that this would work? Any potential problems that I might have doing this? Thank you in advance. -Steve