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.