Mark:

I'm not certain how to do what you ask in VSI, but I've done some of this in Wise Installer for Windows. My problem was that I needed to check a registry key and fail the LaunchConditions if the appropriate value was missing. To do this, I needed to call a C++ dll, that I can send you.

If your logic can wait until later in the process, do the following: (I think case is important, here)
1. create a property call APP_TEST and set it to 1 in the property table
2. create a new row in RegLocator table. Type a unique name to signature_ column. (ex. SearchReg)
3. enter a value for the root column from the following list. Root is predefined root key for the registry value
0: hkey_classes_root
1: hkey_current_user
2: hkey_local_machine
3: hkey_users

4. type the key you want to read in the key column
5. enter the registry value name to name column.
6. enter "2" to type column
7. go to AppSEarch table and create new row. enter a property name (APP_TEST) to store the registry key value.
8. Use the Signature_ value (SearchReg in example) in Signature column.

The rigistry-value will be store in the property when the appsearch-action is executed (at the beginning of the installation ... before a dialog is shown)
(At least in WFWI)

WFWI was $795.00. I found it easier to learn than the InstallShield product. On Win2000, there are many "gottcha's" regarding access to keys in certain hives. The app needs to be run by a user with administrative privledges for some of them. I'd have to check which ones.

HTH