Ya really want to know?
Okay, here's the original frame I worked with:
It's taken from a home recorded DVD of the clickit to pickit showing of "Christmas" last spring.
And here's the finished product:
I used Photoshop Elements 1.0, but just about any version or flavor of photoshop will work the same. I made multiple layers of Kim and Ron, separated their heads, bodies, etc., positioned everything so it looked about right. Ron's gotten taller relative to Kim since "Christmas" (another clue for not putting this ep in junior year, folks! Look how much taller Kim is in the original! At the end of season 2 she's level with Ron, and in season 3, he's taller.)
Then, on a new layer, I redrew and recolored everything. Notice how my lines are relatively thinner than the original (especially with Kim and Ron enlarged). The background's from "So the Drama," the scene where Kim's trying to talk to Dad about boys and dating. I added the Christmas lights.
The other drawing, "Ron's Dorm Room," combined a background I made in photoshop with an original pencil drawing digitally redrawn. Trace Kim and Ron enough times, and really, drawing them becomes easy.
The secret to any of this is command +, which enlarges the view of the picture I'm working on. At 400%, it's easy to have total control of the paintbrush tool or eraser tool. Even without redrawing, it's not too hard to create a perfect edge!
Here's one of the first modifications I ever did, first the original:
Then the alteration:
Again, I made duplicate layers, carefully erased Kim from one, Ron from the other, slid them together, and foreshortened Kim's left forearm to put her hand on Ron's knee. You can see a bit of fringe around Ron's face overlapping Kim's hair, but it looks a lot like the broadcast compression artifacts around the other lines, so I left it like that.
Note the season 2 outlines, a heavier line with varying thicks and thins. In season 3, the outlines are much thinner, the inner lines in Kim's hair are more likely to be parallel than fanning out as they do here, and overall her hair is less poofed out, at least in closeups. Even when I start with a pencil drawing, you can tell this way if the picture I was studying was a season 2 or 3 Kim!