Farmer,
It could be your ISP. Some will boot you off after a certain amount of time without activity. Your internet connection is not active while you are typing, so it may shut down. My old internet service did this.
Also, Internet Explorer has dial-up settings that will disconnect after a certain length of inactivity. This is a setting that you can adjust yourself, using the Tools on your toolbar.
Click on tools, then internet options. Select the connections tab, make sure your dial-up service is highlighted, then select settings. Then click the Advanced button and a window will open where you can adjust this setting. This works for the newest version of IE.
If you have Netscape, you'll have to have someone else help!
Let us know if this or any of the other suggestions solves your problem. IDShooter