I found these skates used on craigslist for $25. They were a size 10 and I wear a size 11.5 so I couldn't use the boots. I'll try to sell them back on craigslist for what I paid. It's cheaper to buy used skates rather than buy all the parts new online. You need the plates, 8 wheels and 16 bearings. It gets pretty expensive. I will probably buy some 72 mm Sims Snakes wheels later to make them even more awesome.
Remove the insole and unscrew the base plates of each skate. You might want to do one at a time so you can use the old skate as a reference when drilling the holes in you Vans.
Step 2: Remove the Vans insoles
Reach in and take out the insole. You want the bolts to be under the insole for a more comfortable ride. You'll also want to remove the laces.
Step 3: Align the plates
Put the plate on the bottom of your Vans and align them properly. I put the back of the plate almost at the very back of the heel. The front didn't quite make it to the front of the shoe because my plates are size 10 and my shoes are 11.5. I used a clamp to hold the plates in place while drilled the two holes in the heel, then I installed the bolts and drilled the fronts without the clamp. I had to remove the wheels so the drill would line up with the holes. Removing the trucks is another option to get access to the holes.