This process is very simple once you figure out how to run it correctly in 5 easy steps:
1st – install SSRS (Reporting Services 2008) on a computer that it is already part of the SharePoint Farm or install the SharePoint server on it and add it to the farm.
2nd – create and configure the SSRS database in SharePoint integrated mode using Reporting Services Configuration Manager.
3rd – download the SQL Server 2008 Reporting Services Add-in for SharePoint Technologies and install it using the rsSharePoint.msi SKIPCA=1 command on all your SharePoint servers that are part of the Farm and have the Windows SharePoint Services Web Application on them. Chose one server, I prefer one that has Central Admin on it, and run the rsCustomAction.exe /i command that it is available in %Temp% folder.
NOTE: Do not run the rsCustomAction.exe command a second time on any other server as it will fail and then remove the feature that was already installed.
4th – In Central Admin under Application Management -> Reporting Services, grant database access and configure the Reporting Services Web Service.
5th – On the site that you want to use the Reporting Services enable the Report Server Integration site collection feature.
References:
How to: Install or Uninstall the Reporting Services Add-in
How to: Create a Report Server Database (Reporting Services Configuration)
How to: Configure Report Server Integration in SharePoint Central Administration
In The Mix 