<p>I have only been working with sharepoint for three months but right from the start I was told that the SharePoint content db was off limits as MS could change the schema at any time. The recommended route is to use the object model, and in most case I kind of understands that.</p>

<p>Now I need to join some lists in order to present the content grouped by some specific fields. Rather then iterating through each and every list I would prefer to link our own db which resides on the same DB server, to the WSS content DB and just create a view on the tables. This view should be on our DB in order to make such that we don't change ANYTHING on the WSS content DB.</p>

<p>Am I on the route to eternal damnation or not?</p>

Yes, you are. Microsoft is
very
clear that any modifications to the SharePoint tables renders you unsupportable.
Direct modification of the SharePoint database or its data is not recommended because it puts the environment in an unsupported state.
Now, creating a link on your own DB which queries the SharePoint DB is shaky ground. Personally I'd do one of two things:
If this is a mission-critical application, run it past MSFT support.
If it is anything else, just make sure that your view is not locking the DB during querying.
A better strategy might be to iterate the lists and sync it to your own table so you can do whatever kind of data-mining you'd like - if you don't mind whatever lag time your sync routine would need.