As jstarkey says www.dyndns.org is one option. I've used it for about 4 years now and have found the service great, I've used it for websites/email to my dialup and also for static websites so they could have a proper hostname.
They also provide free clients so that you can run servers on dynamic IP addresses (e.g. modem dialups or cheaper broadband isps).
All in all pretty damn good for a free organisation. There are a few others around but dyndns seems to have more domains, although this might have changed now.
If you're not sure what you need post back, DNS can be a very confusing system. Basically you sign up for an account at dyndns, pick a hostname, set it to your computers IP address, then add that hostname to your apache/IIS configuration.