There's a command line utility "host" that will do this for you. I made a little handler ipForHostName() to run the host command and parse the text to return only the ip address...
set hostName to "myhost.dyndns.org"
set ipAddress to ipForHostName(hostName)
do shell script "'/Vine Server.app/OSXvnc-server' -connectHost " & quoted form of ipAddress & " -connectPort 5905"
on ipForHostName(hostName)
try
do shell script "/usr/bin/host " & quoted form of hostName & " | grep \"has address\""
return last word of result
on error
return hostName
end try
end ipForHostName