I'm building a transition plan to move the contents (~120 websites) of
an older server running Windows 2000 to a new server running Windows
2003.

I would like either a) a URL with instructions or b) step by step
instructions on how to migrate the forward DNS zones with a bare
minimum of manual data re-entry.

On occasion I have modified the text file for a zone, advanced the
serial number, and then instructed the MS DNS server to reload the
zone. Ultimately what I would love to do is be able to copy the zone
files to the new machine, turn on the service, and have the DNS server
pick up all of the zones and import them.

Also any gotchas or advice would be helpful. For example, should I be
prepared to increment the serial number of all of my zone files to get
them to "take"? Are there registry key sets that I have to set to get
the DNS server to see the zone files?

You can try this MS page
http://www.microsoft.com/resources/documentation/WindowsServ/2003/all/deployguide/en-us/Default.asp?url=/resources/documentation/WindowsServ/2003/all/deployguide/en-us/dssbf_upwn_overview.asp

http://support.microsoft.com/default.aspx?scid=kb;en-us;280061