hi, i have to set up an ftp server box but i have a problem with domain name configuration

heres how: in first computer (192.168.1.112), which is that server, i'v installed Slackware linux 10 and also proftpd ftp daemon. in second computer (192.168.1.99, "main server", which has http daemon running) has a hostname, say hostname.com. now, i need a hostname ftp.hostname.com (port 21) to connect to first computer's ftp daemon. as you can see, both computers are in local area network.

thanks in advance