Hello,
Computer (No.A) is connected with internet. So I can get the update automatically.
But, Computer (No.B, and No.C ) is not connect with internet. But we use the flash Drive and 3 1/2 Floppy disk. Without antivirus software, No.B & C can get the virus. Already having the antivirus software is out of date. So I want to update them (No.B& C).
How should I do?

Download, copy to flash drive and run on B + C

Download AVG Anti-Virus Definitions January 13, 2008 - Latest free virus definitons for AVG AntiVirus - Softpedia

http://free.grisoft.com/doc/24/lng/us/tpl/v5

If any software need to be install to access the internet, install them and then connect to the internet by using the cable for PC A or if you have wi-fi, u can use it.. There are modems (like the one I have) which can be use connect two PC to the internet..