If you choose item 1, you want tab panel 1 to be the front tab panel and if you select item 2, tab panel 2 should be the front tab panel?
Please explain why you want this effect as there may be simpler ways to get what you want here.
To answer the question, you can use the name box in the inspector's position tab to give each panel an object name. You can give them object names that match the values in your drop down's value list.
Then you can use the OnObjectSave trigger to perform this simple script:
Go to Object [YourTable::YourDropDownField]
You can also use the OnRecordLoad trigger to perform this script to select that panel matching a value previously selected in the drop down.
I am building an estimating database that will have several different types of estimates, for diferent types of work. I was thinking that as I enter the customer information, I would have a field (drop-down list) to determine what type of estimate this would be – type 1, type 2, etc… Then, after choosing what type, a tab panel would appear containing tabs specific to that type. Some of the items on Tab Panel 1 (for Type 1) would not be needed for Type 2.
Sounds like a reasonable user of the example I've already posted. Note that your outer tab control, the one selected by Go to Object, can be given a transparent fill pattern and 0 width border so that it is invisible to the user, but the items inside the tab panel--your type specific set of tabs, are visible and will appear and disappear when go to object selects a different tab.
Here's a demo file of different controlled visibility tricks that includes the invisible tab control trick: https://www.dropbox.com/s/8levaz6deiyzjr8/LayoutObjectVisibilityControlDemo.fp7