Bicycle Mechanics - Dura Ace Components Compatibility with my Tarmac 105?

Totally new at this and I find myself in a funny situation. What I currently have a 2010 Tarmac comp with 105 components. Somebody locally is selling a Roubaix S-Works for soo cheap I NEED to buy it:) I find myself in a situation where I might just ride it and see if I want to keep it. If I would rather keep the Tarmac maybe swap out the parts if its possible? Maybe even sell it if I dont like it? I need to get in contact with this guy I don't even know the size of the Roubaix. His description is "roubaix carbon fiber w/ dura ace components" Hell I might keep em both as is. I test rode a Roubaix and liked it but ended up going with the Tarmac. I like my Tarmac but I rode my friends Allez with Ultegra parts for a week and really liked it, so I am guessing the Dura Ace parts have to be a good upgrage. I searched a bit and didn't find much. I found some website that had some sort of interchange chart but couldn't really understand it. Sorry for being such a noob at this, I will like my other hobbies eventually get their!

The simple answer is yes, for the most part. In detail, you have to know the year of th DA parts. Seems like a small chance the the Roubaix would be the right size. Remember it has a lot taller head tube, for a given size. Not the ticket for a racy fit.

Also keep in mind that bikes drop in value very fast, since they can be had for 25% off or more just at an end of year sale. Some people can abuse a bike so much that it's not worth half price after a year.

Cool thanks! From what I made out of it guy dropped a lot of money never used it and now wants to sell it cheap. I think its a newer bike maybe 08ish? I'll find that out later. If he is seriously about the price he is basically giving it away.

I just about gave away my two LOOK 585 bikes. 2006 and 2007 frames, both flawless with Record 11 drivetrains. Fulcrum Zero wheels on one and Powertap SL on the other. $4800 for both.

Keep in mind that the compatibility of parts depends more on the number of cogs (8-speed, 9-speed, 10-speed) than on the group level. A complete Dura-Ace group could be used to replace a complete 105 goup. But if the D-A is well worn and of an older generation then it may be less valuable than 10-speed 105.

Are you asking whether you can hang the DA group from the new bike on the old bike? Yes, without any problem.
Or are you asking whether DA components are compatible with 105? Yes, if they're all 10-speed. If not, you may have some problems. Or not. (My CX bike is a mix of DA, Ultegra, 105, and RSX (!))

Also DA is not always an upgrade. It is the new and improved model not necessarily the most reliable.

Thanks for the info everybody but I talked to him today and he had just sold it. It was older than I thought too, his was a 05 model but only wanted $950 for it. O well I will keep enjoying my Tarmac! Once again thanks everybody!