chopping help!!

I'm trying to do a photochop here, and I realized I don't really have a clue what I'm doing... Well, that's not entirely true, I've done lots of stuff with PSP, but this is alot more complex....

What I'm trying to do is photo chop a different front end onto my car... I have two pics of what I'm trying to accomplish, non chopped, real life pics...

Here they are

http://members.rennlist.com/sbcspeed/924with951airdam.jpg
http://www.911virgin.com/big924turbo1.jpg

That's the air dam from a 944 Turbo, this car

http://jimweb.free.fr/front_angle.jpg
http://www.ipa.net/~warpspd/side3.jpg


On a 924, this car...

http://www.pca.org/panorama/images/924/9249.jpg
http://www.bodyline.on.ca/PageMill_Images/porshe.jpg

The only difference is teh width of the fenders, and the width of the air dam.... does anyone have any good tips about how to do this? Skewing the angles?