I do my seats differently from everyone I see... they usually work OK though, maybe I'll make a little tut.
here's the seat I put in the Z... i usually get compliments on them.
These were done by:
-Finding seats (hardest part)
-Cutting out the seat from whatever picture you find it in... I usually use the same
Sparco seat, just change color/accessories.
-I fit the entire seat overtop of the car, trying to imagine how they would fit in the car...to give me a measuer of how big they should be... when positioning, remember the new seats will be where the old seats are, so they should roughly cover the old seat headrest
-Now that the seats are ontop of the car, and look completely weird... I turn that layer off and use lasso tool to select anything that will obstruct the view of the seats... like the car (duh), mirrors, inside mirrors, steering wheel, dashboard, solid tinting on windshield, etc... Then I turn the layer back on and "Select>Inverse" then delete. It should leav you with the visible parts of each seat.
-Now I create a new layer and put it ontop of the seats. Name it "OVERLAY" or soemthing. Now using the selection tool, I would select one or two colors that are some of the lightest colors. Now hit CTRL+the seat layer to get the selection of the seats. Now using that selection, fill your overlay layer with that color/s.
-Now that the seats still look weird, lower the opacity of the overlay layer. Mine usually go to about 65-85%...depending on what looks good.
-Well... pretty much done. It is possible their is a dark line around the whole seat, and this is because of how photoshop does it's edges when filling in an area, it can go a little short. If the dark edges appear, just make the selection of your seats like before... then fill the overlay layer 2-3 times again over top each other... this sort of forces the 'paint' to the edges so you cover the seat... do no more than 3 times though, or you will get a very sharp edge which will also look bad.
Hope this helps... You can use it for anything, rollcage, people, spoilers...etc...