Ok, so both apps use shared DDLs probably located in the c:\winnt\ or c:\winnt\system32\ directories. When you install the first app, it places the shared DLLs in one of the directories mentioned. When you install the second app, it overwrites one or more of the DLLs and makes the first app unusable.

Here's my suggestion: Install the first app, find out which DLLs it inserts into the c:\winnt\ or c:\winnt\system32 directories. Copy the DLLs into the the app's directory (c:\program files\etheral\) and try to run the application. If it doesn't work, ok so this method doesn't work at all . But if it works, you can install the second app, and it's probably gonna work also!

Actually what I'm saying here is that many applications look for shared dll's in their own directory, if they can't find any they will look for them in the system directories. Some apps created with Visual Studio work this way (if I remember correct). But then again there can be other ways.