This video shows how to get more value on your GoDaddy account. You have to have a deluxe account to share domains. You have to pay an extra $2 a month to get this account. Once you sign in go to "hosting" then my "hosting account". To add another domain you move it over to a new folder then put the site files in there. To do this, click add domain then go to bulk. Then create a folder and name it what you desire. Sometimes the file folder doesn't always appear immediately, but it is there, it just take a little while. Hit upload to upload site files. Browse then select the desired files and hit upload. After that is successful, move all the rest of your files into that file.
Oh... and if you're working from home these days, be sure to check out Gadget Hacks' Working-From-Home Essentials.