I ran across a well written article on creating an MSDE msi embedded
installation but it seems to be missing a critical step. The purpose of an
embedded installation should be based on a condition (exmple
\Software\Microsoft\Microsoft Sql Server\Instancename). If the condition
exists, there would be no need to call the embedded installation. The above
example would be a Registry Target that I would name "MSDEInstalled". If
the registry item did not exist the installer should know how to call the
embedded msi to install MSDE.

I am confused as to whether this Custom Action would be a Type 39 or a Type
50. I made a guess that it is a type 39, but the code I have put in to
create the condition and then based on the condition - to call or not call
the embedded MSDE installation - is not clear to me.

Here is my best approximation. If someone can help a bit I would appreciate
it. If you look closely you'll see I am rather lost on this Custom Action
property.
--
Regards,
Jamie

Assume that I have defined a registry key and called it MSDEInstalled which
is the key for my instance:
HKLM\SOFTWARE\Microsoft\Microsoft SQL Server\MyInstance. Also assume that I
am defining this as a type 39 Custom Action.

InstallMSDE.vbs

Option Expicit
dim inst, rec, sqlquery, database, view

sqlquery="SELECT 'MSDEInstalled' FROM _Storages"

set inst=Createobject("WindowsInstaller.Installer")
"" lookup path to parent MSI
set database=inst.OpenDatabase("<path to Parent MSI>",1)
set view=database.openview(sqlQuery)
set rec=inst.createrecord(2)
rec.stringdata(1)="MSDEInstalled"
view.execute rec

If rec.value then
UINT MsiDoAction (MSIHANDLE hInstall, LPCTSTR szAction)

""next line would set the condition true so that the calling routine can
continue

The following link will take you to the article I am referring to: