Seeing a list of SQL Server Reporting Services reports from Report Explorer WebPart is pretty simple.  Set the “Report Manager URL” property to the URL of the report manager.  In my case http://localhost/Reports.  What I couldn’t figure out for a while was viewing a report that I clicked on from the Report Explorer WebPart in the report viewer WebPart.  This is actually simple once I figured it out.  Here are the steps.  This assumes both web parts are added to the same page.  And the Report Explorer is configured.  For help on that click HERE.

1) Click Edit “Site Actions” top right of page
2) Edit Page
3) On the Report Viewer WebPart click edit
4) Go to connections from the popup menu (follow next path in popup menu)
5) Connections -> Get Report From -> Report Explorer
6) Exit Edit Mode, top right of page

There you go you should now be able to click on a report in the Report Explorer and view it in the Report Viewer WebPart.  Hope that helps.

One HUGE problem I have run into while messing with SharePoint Services and Reporting Services is lack of 3.0 information. 

I have been working the last 2 days on getting SSRS and WSS 3.0 both working and getting them to work together.  I am now a bit closer to this with the addition of adding the Reporting Services WebParts to SharePoint then getting a list of reports.  Here are the steps I followed to get it all working. (note: yours could be different)

1) Install SQL Server 2005 and with Reporting Services (Advanced SQL Server Express)
2) Install SQL Server Toolkit ( with Business Intelligence Developer Studio, just a good idea)
3) Run the Report Services Configuration Tool and set the web application to be under the SharePoint.  Pay attention to this post when doing this step.
4) Create a new Reporting Services Database.  (Look at this post)
5) I found the .cab file for the Reporting Services Web Parts to add to SharePoint  on my machine here: “C:\Program Files\Microsoft SQL Server\90\Tools\Reporting Services\SharePoint”
6) With the cab file I run this command using stsadm.exe from this folder “C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN”
7) Once that is complete open up SharePoint in your browser and add the Report Explorer WebPart.
Click edit web part -> modify shared web part on the Report Explorer web part.
9) added the following URL to “Report Manager URL” http://localhost/Reports
10) hit ok button. 
11) See a list of available reports.

What I don’t have figured out yet is viewing these reports in the report viewer web part.  I also don’t know if that is even possible. yet.  So stay tuned.