#if and Compiler switches

Question

I'm trying to get my project to evaluate a compiler switch (/define:ORACLE) using a #if.

The syntax I'm using is:

#if ORACLE
using DAL=mydll.Oracle;
#else
using DAL=mydll.SqlServer;
#endif

The problem is that this always drops into the SQL server leg, anf ideas on how to get it to use the Oracle leg??

Using Visual Studio 2005 & C#

Thanks Ash...