ACDSee Photo Manager keeps an internal database about all the files and organization. That organization (ACDSee Database) needs to be accesible by both computers. The External Hard Drive is recognized by its volume ID so it knows where the files are. So the trick is to place the internal database is a spot accessible to both computers which is namely the External Hard Drive.

Directions on working on 2 computers with a external hard drive between them:

Important: If you want to share your database between a Vista & XP computers, their is some extra steps that NEED to be done.

1. Place all your digital kits and images on the External Hard Drive (EHD). To do this: How to Move Organized Digital Kits
2. The next step is getting the ACDSee database moved on to your EHD:
3. Exit ACDSee Photo Manager
4. Connect your EHD
   
5. Open Windows Explorer
6. Browse to this location:
   
   1. In Version 9 on XP: In Windows Explorer go to this location: "C:\Documents and Settings\YOUR_USER_NAME\Local Settings\Application Data\ACD Systems\Catalogs\90"
   2. In Version 10 on XP: In Windows Explorer go to this location: "C:\Documents and Settings\YOUR_USER_NAME\Local Settings\Application Data\ACD Systems\Catalogs\100"
   3. In Version 9 on Vista: Go to this location: My Computer, C:\Users\[Your User Name]\AppData\Local\ACD Systems\Catalogs\90
   4. In Version 10 on Vista: Go to this location: My Computer, C:\Users\[Your User Name]\AppData\Local\ACD Systems\Catalogs\100
   5. XP Tips: View your Local Settings Folder (for XP)
   6. Vista Tips: How to view your AppData folder on Vista
7. Select the Default folder and choose Edit | Copy (or Ctrl-c)
8. Still in Windows Explorer, browse to the EHD.
   
9. Make a new folder called ACDSee Database
10. Click on the new folder you just created, and choose Edit | Paste (or Ctrl-v) to copy the Default folder (Database) to the EHD.
11. Start ACDSee Photo Manager (This step is what I call "Pointing to the database")
    1. Click on Tools | Options
    2. Click on the Database
    3. At the end of the path of the database, click on the icon and browse to your EHD. On the EHD select this path: ACDSee Database\Default
12. Restart Photo Manager and make sure your categories are there and you can search for your images and go to file takes you to your files.
13. Close down ACDSee Photo Manager and unplug your EHD. Connect the EHD to the second computer.
    
14. If BOTH computers are XP, or BOTH are Vista, or the original computer was Vista: then repeat step 11 & 12 on the second computer.
15. If the first computer is XP and the second computer is Vista, then do the following:
    
    1. Close Photo Manager
       
    2. Using Windows Explorer, browse to the EHD:\ACDSee Database folder.
    3. Select the Default folder and choose Edit | Copy (or Ctrl-c)
    4. Browse to:
       
       1. In Version 9 on Vista: Go to this location: My Computer, C:\Users\[Your User Name]\AppData\Local\ACD Systems\Catalogs\90
       2. In Version 10 on Vista: Go to this location: My Computer, C:\Users\[Your User Name]\AppData\Local\ACD Systems\Catalogs\100
    5. Right click on the Default folder and rename the Default folder to Default-old
    6. Choose Edit | Paste (or Ctrl-v) to copy in Default folder (Database) from the EHD.
    7. Start Photo Manager, make sure your categories are there and you can search.
    8. Close Photo Manager
    9. Browse to same location on Vista as step #4 above.
    10. Select the Default folder and choose Edit | Copy (or Ctrl-c)
    11. Browse to the EHD:\ACDSee Database folder.
    12. Delete the Default folder here.
    13. Choose Edit | Paste (or Ctrl-v) to copy in Default folder (Database) from the Vista computer.
    14. Then do steps 11 & 12 above.
    15. Lastly, always optimize from the Vista computer!!

Word of Caution: Your database for ACDSee is now stored on EHD. If you start ACDSee and the EHD is disconnected you will receive an error message "Can not connect to database" So always connect the EHD before starting ACDSee Photo Manager.