Connecting To Oracle 10g Database Using VBA?

I need to connect to an Oracle 10g database using vba. Google has loads of snipets of code but I don't seem to be able to get it to quite work correctly.

This is what I have:

Code:
Sub ADOExcelSQLServer()
Dim Cn As ADODB.Connection
Dim Server_Name As String
Dim Database_Name As String
Dim User_ID As String
Dim Password As String
Dim SQLStr As String

[code]....

When the connection attempts to open (red code) I get the following error:

Run-time error '-2147467259 (80004005)':
[Microsoft][ODBC Driver Manager] Driver's SQLSetConnectAttr failed

My best guess is that I do not have the correct drivers installed... If this is the case which drivers do I need and where can you get them from?