To set Dreamweaver to open the images in ACDSee, you need to set ACDSee as the file Editor for that image type. Here's how:
Go to the Edit menu and click on Preferences at the bottom of the menu.
Under Category on the left click on File Types / Editors
On the right side you will now see two lists, one showing the file types that Dreamweaver can recognize and one showing which program is used to edit that file type. Click on each of the file types in the left window and then edit the program associated with that file type in the right window. You will need to do this for each needed file type separately. The ones you want are .png .jpg .gif
To set the program associated with the file type, first click on the + button and locate the program you want to use. The file will be in your Programs folder, probably in the ACD Systems folder, then in the ACDSee folder, then in the 8.0 folder, probably named ACDSee8.exe. I don't have version 8 here but I am guessing that I am right on all this.
You will now see ACDSee in your list of Editors for the file type. Now select ACDSee in the list and click on the Make Primary button. Once you have done this for all three file types click on the OK button to close the dialog box and you should be all set.