<Limit GET> order deny,allow allow from 123.456.789.0 allow from 123.45.67 deny from all </Limit>
That would allow the IP address 123.456.789.0 and any IP addresses starting with 123.456.67 and deny access to everyone else.
Edit: Also do NOT put a space before or after the comma in "allow,deny" as the server will consider this as a syntax error and will not allow anyone to access the directory.