Symantec Norton Internet Security 2007 Full Version for PC Review

One of my acquaintance sent us an e-mail which contained a computer virus.  This software wiped it out in a second automatically without my knowledge.  What a wonderful Anti-Virus software is! 

However, it slows down any computer operations dramatically, especially, whenever I open any file of MS word, or Excel and so on. 

My another computer is very old and has a small hard disk.  My second computer has been occupied by this software.  I can not install any software there.  This Anti-Virus software is so large and eats up PC resources.  Of course, it slows down mortally any computer operations of this old computer.