Grisoft provides free programs for home use. As it says on their site: AVG Anti-Virus Free which includes AVG Anti-Spyware Free and AVG Anti-Rootkit are for private, non-commercial, single home computer use only.

The newest version as of Dec 08 is ver 8 and will not run on older versions of windows. You need XP SP 2 or higher.
As of December 2009, the current version is 9. They keep changing the pages but the principle is the same.
As with most programs they offer the pro version free but with a catch. Buyer beware!

The AVG programs must be downloaded by each customer. They are free, but you may have to register to get the programs to work. Follow these instructions to get the program:

Note: these instructions apply to IE 6. Now with IE8 and 9, the method is the same but the windows look different.

1. Go to free.grisoft.com. You will see 2programs listed.
AVG Anti-Virus Free
AVG Anti-Rootkit Free

2. Click on the AVG Anti-Virus Free link. The next page will display this chart which shows the features of the free version vs the pay versions. Click the Download link at the bottom of the Free column.

3. Follow the instructions to download and install the programs.

When the download starts you will see this dialog box (except it will show a newer version). Select Save.

The next box you see is asking you for a location to place the file. Many suggest using the desktop. I prefer to put it in it's own folder under My Documents/ My Downloads. If you don't have a My Downloads folder, create it. Then create a folder under it called AVG.

Make sure the folder you want is in the top box "Save In". Then select Save and you get the next dialog box that shows progress of the download. Be sure you UNcheck the box "Close this dialog box when download completes" because you will open the file from this box. If it closes, you must go find the downloaded file and open it from there. Thats why it is recommended to use the desktop since it is easy to find after downloading. They tell you to just delete the downloaded file after you install it. I like to keep it and I don't like my desktop cluttered.

Click Run & just follow the prompts. When asked if you want to download the latest database, do so. After that, the program will keep you up to date automatically.

You may see various dialog boxes. Read and answer them.