The short answer. Don?t install more than one anti-virus. They may conflict, and will provide less protection, not more.
The longer, technically correct answer. Yes, it is possible in most cases to install more than one anti-virus. Provided that only one real-time scanner is active at a time, and the others are used only to scan on demand. However, pre-Windows Vista, all anti-virus programs made changes to the Windows kernel. Or, the very core of the operating system. One application doesn?t know what changes the other has made, and they are likely trying to affect the same code. This can lead to system slow-downs, instability, and crashes. Or even the loss of all anti-virus protection.
Keep it simple. Chose one anti-virus that you like, and stick with it.