Start the computer in Safe Mode, then run the Norton AntiVirus and have the Trojan removed. Be sure to turn off the System Restore.
First, turn off System Restore.
To turn off Windows XP System Restore
1. Click the Start button.
2. Right-click My Computer, and then click Properties.
3. On the System Restore tab, check Turn off System Restore or Turn off System Restore on all drives.
4. Click Apply.
5. Click Yes to the message asking if you want to turn off System Restore.
6. Click OK.
7. Restart the computer and follow the instructions in the next section to run the computer in Safe Mode.
To get into the XP Safe mode, as the computer is booting press and hold your "F8 Key" which should bring up the "Windows Advanced Options Menu". Use your arrow keys to move to "Safe Mode" and press your Enter key.
Note: With some computers if you press and hold a key as the computer is booting you will get a stuck key message. If this occurs, instead of pressing and holding the "F8 key", tap the "F8 key" continuously until you get the startup menu.
Once you're in Safe Mode, run the Norton Antivirus and allow it to remove the infected files. It should now be able to do this. Once the infected files are removed, restart the computer. It will start in Normal Mode automatically.
To turn on Windows XP System Restore:
1. Follow the steps in the first section, but in step 3, uncheck the "Turn off System Restore" option.
2. Then click OK.
3. Create new System Restore points:
4. Click Start
5. Click Run
6. Type in: msconfig
7. Click OK
8. Click the System Restore button.
9. Select "Create new System Restore point".
10. Give the Restore a name (Like "After Trojan Removal"
11. OK your selection and restart the computer when prompted.
Some notes: (Following copied from the Norton AntiVirus Help section here.
You can use System Restore to restore the computer to a previous state, using the backups that it makes of selected system files and program files.
While this is a desirable feature, in some cases it should be temporarily turned off. For example, if the computer is infected with a virus, then it is possible that the virus could be backed up by System Restore. By default, Windows prevents System Restore from being modified by outside programs. As a result, there is the possibility that you could restore a virus-infected file, or that the on-line scanners would detect the virus in that location.
Disabling System Restore does not delete or remove any of your personal data from your computer. The only files removed are those that System Restore created, the restore points.