The following definitions explain the difference between virus and spyware:

Virus:

A program or piece of code that is loaded onto the computer without the person's knowledge and runs against his or her wishes. Viruses can also replicate themselves. All computer viruses are manmade. A simple virus that can make a copy of itself over and over again is relatively easy to produce. Even such a simple virus is dangerous because it will quickly use all available memory and bring the system to a halt. An even more dangerous type of virus is one capable of transmitting itself across networks and bypassing

Antivirus:

A utility that searches a hard disk for viruses and removes any that are found. Most antivirus programs include an auto-update feature that enables the program to download profiles of new viruses so that it can check for the new viruses as soon as they are discovered. 

Spyware:

Spyware is any technology that aids in gathering information about a person or organization without his or her knowledge. On the Internet (where it is sometimes called a spybot or tracking software), spyware is programming that is put in someone's computer to secretly gather information about the user and relay it to advertisers or other interested parties. Spyware can get in a computer as a software virus or as the result of installing a new program.

Anti-Spyware:

Also called Spyware removal. This is a program to remove spyware from the computer. The following link provide more information on Microsoft's anti-spyware program: Microsoft Anti-Spyware