The point is simple -- your $Conn->Open(...) opens database correctly, but your code just did not noticed that.

Try in your code for example following:

$Conn->Open("DSN=ENG_DB;UID=enguser;PWD=yt12xcj");
print '[[',$Conn->{DefaultDatabase},"]]\n";
[download]

but when you intentionally break your code to, say,

$Conn->Open("DSN=BADBADENG_DB;UID=enguser;PWD=yt12xcj");
print '[[',$Conn->{DefaultDatabase},"]]\n";
[download]

you'll see a difference!

I just modelled this situation on my computer.

BTW when searched a documentation, I noticed that VB sample code from MSDN does not checks for return code, it probably relies on On Error statement

Courage, the Cowardly Dog