Well, first of all I would suggest that you upgrade your version of Apache. Newer versions (>= 1.3.19) allow for wildcards in your httpd.conf file. Here is a snippet of mine:

NameVirtualHost *

<VirtualHost *>
        DocumentRoot /web/htdocs/mrnick
        ServerName www.mrnick.binary9.net
        CustomLog logs/mrnick.log combined
        CustomLog logs/access.log mine
</VirtualHost>

<VirtualHost *>
        DocumentRoot /web/htdocs/radio
        CustomLog logs/radio.log combined
        Servername ourthing.radio.binary9.net
        CustomLog logs/access.log mine
</VirtualHost>
[download]

Notice how no IP addresses are directly coded into the file? This would allow you NOT to have to update it everytime you change IP's. You might have to apachectl restart it after it has changed, though. If you are using dhcpc, there is a file (/etc/dhcpc/dhcpcd-eth0.exe) that is run when your IP address changes. Just restart your server from in there.

mr.nick ...