I have a friend who is selling an XLR, and I want to buy it. Its a 2004. I was wondering, because the cars have seemed to change so little, if I could possibly swap out some parts so I would have the newer nav system as well as OnStar from an 08 or 09 model? Thanks!

I ain't no mechanic, but I suspect you can do it for a few thousand $$--probably close to $8,000 or so. Cheaper to buy a newer version. Electronics are expensive, very complicated, and in many cases proprietary to individual model years. (This is what I have heard/seen with this question re several diff makes, models of vehicles.)

I honestly think you will be spinning your wheels attempting this. You would likely create electrical headaches that no one could resolve since the changes would not have been tested by anyone at GM. No documentation for your changes = multiple and unexpected problems.