Well, do you have access to your networks router? You can always install a program such as WAMP (wampserver.com) or XAMPP (apachefriends.org/en/xampp.html) This will provide you with a Windows environment for Apache, MySQL and PHP, and let you host from your computer, so long as it has an active internet connection, and you don't turn off your computer (can't have a server online if the computer isn't, haha) You will need to forward ports to your computer, via your router, to allow outside access. Keep in mind however, the speed of your website will depend on how much traffic you're getting, and what type of internet you have. If you have a Cable (10mbps+) line, you should be able to handle a user or two per second, but any less than that and your site will be slow to the outside world. Read up on how to forward ports for your particular router, or let us know which you have and I'm sure we can assist you further. Another thing you will want to keep in mind, is if you already have a static IP address, you should utilize a free nameserver (Namecheap.com provides a host record modification tool that I really like), or if you have a dynamic dns, or even prefer to use them as a lot of people do, dyndns.com provides a name server for multiple IPs, or just a single one if you want to utilize them. There are a lot of options for you to host nameservers outside of your network. Hopefully this has been helpful.
Well, you will need software. The Apache software is most popular among servers. Then, you'll have to install other things such PHP and mySQL. It may be wise to check with your ISP before you begin hosting your own website from your own system. They may not allow it.
That is interesting, i didn't know you could do this, im going to look into it but i'm guessing it will be costly, with all the software involved i mean.
You can do it as teh second person said, but I highly advice you don't. You can be charged for over usage charges, your computer may become slower, and it means your computer must be online all day and night!
Agreed Most if not all ISP's block outbound port 80, and/or it specifically states in the end user agreement that websites cannot be hosted. However also a lot of ISP's look the other way on this subject, meaning they won't do anything about it, but there's still a risk.