instead of buying a domain you can use a free service like no-ip.com or dyndns.org. they redirect users to the right address if you have a dynamic ip. You use an IP updater program that checks a server every few minutes to see if your IP has changed. if it does it logs into your no-ip or dyndns account and updates the IP adress. instead of users connecting to say 217.17.27.46 they would use john.dyndns.org
instructions are at
http://www.dyndns.org/,