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To install SharePoint Portal Server on the same server as Project Server, you must follow a structured approach by completing these high-level steps in this exact order:
1. Install SharePoint Portal Server 2003
2. Run WSSWIZ.exe
3. Create a Portal site on the default web site
4. Create a WSS site
5. Install Project Server
For detailed instructions on installing SharePoint Portal Server and Project Server together, see the following KB article:
http://support.microsoft.com/default.aspx?kbid=840701