Actually, I think I might have figured out a way to do this. Not sure if it's the best way but I know it's working very well for me.
Here's what I did and please tell me if you see any ways this could be improved.
First, I have my Digital File Pro set to create two versions of the uploaded image. By default it adds the _thumb to the [FileName]. But I removed that and simply had it upload both a 800 pixel wide filename.jpg and a 150 pixel wide filename.jpg. But the smaller one is uploaded to /images/thumbs/. So it only requires one column in the table since this column only includes the filename and not the path.
Then, in my repeat region table, I have the thumbnail image placeholder dynamically linked to the smaller image using the /images/thumbs/ as the source path.
Within my popup code, I only reference the larger image by the same filename and record set column name but with /images/ as the source path.
That was all working fine but I needed something to call the larger images to be preloaded in the background. So I used the Dreamweaver behavior "Preload Images" and first selected the thumbnail to generate all the code and links.
Finally I removed the /thumbs/ part from the path for just the preload call. So the page shows the thumbnails and loads fast. But the DW code thinks it's loading the same image but it's coming from the /images/ folder.
This is what it looks like on the thumbnail minus the popup code. And minus the DW script at in the head of the page.
<img src="/images/thumbs/<?php echo $row_rsMyrecords['image1']; ?>"
alt="image1" name="image1" width="150" height="149" border="0"
onload="MM_preloadImages('/imgages/<?php echo $row_rsMyrecords['image1']; ?>')" />