Yes, the “myList” variable is a generic list that will be read and each item inserted into the popup menu. If using the syntax from your first post, this would actually be changed to “dlist” I believe.
These are just names I gave the objects in the sample code to illustrate the references I was making. You can change them to whatever you want in interface builder and then make sure to reference them as such in your scripts. Also, make sure you are talking about each item’s applescript name and not it’s title. Click on an item in IB and then select “Tools > Show Info” (cmd-shft-i). Then select “Applescript” (cmd-7) from the popup button in the info window. The window’s title and AS name are different, and this is an important distinction.
When you use a repeat loop, one of the standard syntax forms is repeating through a list of items, automatically evaluating each item as it is encountered. For example, in the case of this repeat loop…
…the loop repeats for every item in the list ‘myList’, and places the contents of the current list item into the variable ‘tempItem’. Assuming the sample code, on the first loop of the repeat the contents of tempItem would be “Item 1” (the contents of the first item of myList). On the second loop, the contents of tempItem would be “Item 2”… and this would continue through all the items in the list.
How and when you populate your list is up to you. You could do it on ‘launch’ of the app, on ‘will open’ of the window, at the press of a button, etc. I will place the code which populates the button into a subroutine so you can use it anywhere, and create a few connections to it so you can see how it’s used. I changed a few variables in the code to better reflect changes relavent to your setup. See the comments in the code for more content-specific info.
--> Attach this to the 'choose menu item' handler of the popup button
--> This will receive the selection of a menu item by it's name
on choose menu item theObject
set theDisk to (name of current menu item of theObject)
display dialog theDisk --> For testing only
--> insert your shell script code here
end choose menu item
--> Attached to a button named "populate" that updates the current list of disks
on clicked theObject
if name of theObject is "populate" then
populatePopup()
end if
end clicked
--> Attached to the window named "Window"...
--> ...which assumably contains a popup button named "popupButton" that lists the disks
--> Populates the popup button every time the window opens
on will open theObject
if name of theObject is "Window" then
populatePopup()
end if
end will open
--> A subroutine which can be called from any handler
--> Immediately updates the contents of the popup button with the current disks
to populatePopup()
set excludeDisks to {"BootCD", "Network"}
tell application "Finder" to set dlist to (name of every disk whose name is not in excludeDisks) as list
tell menu of popup button "popupButton" of window "Window"
try --> Try to delete any existing menu items
delete every menu item
end try
repeat with tempd in dlist
make new menu item at end of menu items with properties {name:tempd, title:tempd, enabled:true}
end repeat
end tell
end populatePopup
Hopefully, I have made this easier to understand and implement, and not more complicated. 
Take care…
j