What you need to do to using the SharePoint add-in for SQL2005:

Install ref 1

1. Install SQL 2005 and reporting service, then patch the sp2 for SQL 2005.
2. Install WSS 3.0 or MOSS 2007
3. Install the Share Point Reporting Service Add-in for SQL Server 2005.
4. Configure reporting service to integrate with WSS
5. Configure the WSS site in the central Administration site and activate the site collection feature in the deployed web application.

Use, the add-in we just installed provide a great feature, including a web part, three content types and several pages to maintain.

1. In the Moss 2007, just create a report site template.
2. Under pure WSS environment, create a document library, and then change the content types. Include report, data source and report builder module content types.
3. Create a data source file, just put the right connection string in the edit page and provide the right user account that have permission with the target data base. For example, you could add a connection string which point to the Adventure Works sample database.
4. Create a report. In the report document library, click new to add a new item. By doing this, the report builder application will be invoked. Or you could just upload a pre-built report. Eg. The Adventure Works sample report.
5. If add a adventure works sample report, you have to edit the report by clicking the "Manage data source" menu in the report context menu. In the edit page, choose the Adventure Work data source and point it to the one that you just created.
6. The report could be see when you click it, however you could do more.
7. Create a new page, and add the report viewer web part which is provide along by the add-in. Change the report file to the one you just created in step 5. Now you have a web part page with a reporting service web part.

Reference

1. Microsoft SQL Server Reporting Services - Installation and Configuration Guide for SharePoint Integration Mode. http://blogs.msdn.com/sharepoint/attachment/4194088.ashx
2. 2007 Microsoft Office System Business Intelligence Integration with SQL Server 2005