I have been doing some sample projects in WCF (hosted in IIS 6.0), and today I was trying to debug the service like I have done with web services and ASP.net but with no luck, the break point does not get hit at all !!!, After some goggling found out that direct debugging of projects in the same solution is not possible with WCF.
The work around is to run your client and then attach to the external process aspnet_wp.exe and your break points will hit.
Debugging of WCF services in the same solution will be possible in VS 2008.