Depends on what you want to host.
If it's just hosting a website you're working on locally before you go live with it or something, yes you can do that no problem. The best server software is usually free.
If it's something like hosting your own email or a site for others to use, not really, since the upload speed from a 56k modem is only 2.8k/second. Your upload speed would be the user's download speed. Needless to say someone on DSL wouldn't be very impressed with your website if he could only load it at half-dialup speed
.
There's also the problem of a static IP address. All
http://www.pcmech.com does is resolve to a public static IP address that is this site's true address. Without a static IP address your server would only be accessible by the public until you got disconnected and your IP address changed (since most dialup providers use dynamically assigned IP addresses, i.e. you're given one from a pool that they have each time you connect, and it'll be different every time).