linking databases for reporting
If you have the option of moving the data into another database I would begin looking at using a star schema.  Here is a website that might help you begin research 

http://www.ciobriefings.com/Publications/WhitePapers/DesigningtheStarSchemaDatabase/tabid/101/Default.aspx 

Star schemas are built specificly for the fast retrieval of large amounts of data and are very good at aggregating that data over time.  Plus having the data seperated from your OLTP database means that there are not as many draw backs to adding indexes.  What's more having your data layed out in a Star Schema sets you up to be for creating data cubes with SSAS in the future; although, you do not need a cube to interface with the data.