Editor's Note: This works for all versions of AIM for Windows from 5.9.6089 and below! A good alternative to Hex Workshop is HxDen.

This works for all versions from 4.8.2616 and below.

1: You will need a hex editor. I recommend you get HexWorkshop. Download it and install it.

2: Go to where you installed AIM (Most likely C:\Program Files\AIM95)
    Copy all the contents of the folder and go back a folder, make another folder, name it AIM95-2 or whatever you want.

3: Opened the hex editor you downloaded (or HexWorkshop).

4: In the menu at the top, click Edit > Find, you will see a few options:
    Find What:
    Type:
    Value:

    In the "Type" pulldown menu, select "Text String"
    and in the "Value" text box, enter "Oscar_AppMutex"

    When it finds it, you should see something like:

    _Oscar_AppMutex.-I"%s"

    Now, pay close attention: After the "AppMutex", overwrite the . with a 2, or whatever.
    Making it look like:
    _Oscar_AppMutex2-I"%s"

5: Now, go to File -> Save. Close HexWorkshop.

If you did this correctly, you should now be able to open up:

C:\Program Files\AIM95\aim.exe
and
C:\Program Files\AIM95-2\aim.exe

At the same time, you may do this as many times as you want, but you can only sign on 10 SNs per IP. (You can use proxies to get around this.)