If anti virus software is installed on your computer that won't help to avoid this problem. There are no any detection definition on that particular malware executable files in your USB drives. Executable files will be activated once Windows autorun feature enabled when USB plug-in.
Below is the steps on how to disable "Autorun" for removable devices in Windows XP.
1. Launch Run dialog box by pressing win + r , then type gpedit.msc and press Enter.
2. Navigate to Computer Configuration --> Administrative Templates --> System
3. Double click on "Turn off Autoplay", choose "Enabled" and make sure select "All drives" from the drop down menu Autoplay on option.
4. Click "Apply" to end your configuration here. Have fun!