There's probably a bunch of videos on youtube.
You need one of these to get the trim off. You may have to find one on Ebay though. Gearwrench (who own KD Tools) doesn't list it anymore.
You slide the hook under the trim and unhook the clips. It takes a little patience, but this is the best tool I've ever found to do the job.
I like using piano wire to cut the old ribbon. I get a piece long enough to put through the edge of the window on the top and then push back it out through the edge on the bottom. I can then stand outside the car and saw through it.
Harbor Fright has a kit now. I've never used it, but it looks like it would work nicely.
Once you've "sawed" your way around the window, get a helper to remove the glass.
Scrap the old ribbon off the glass and window frame. This is a good time to replace all the old molding clips.
Lay the new ribbon in and put the window back in. You'll have to use some rubber blocks at the base of the glass to push it up into position. They used to come with the ribbon kit.
Push on the window gingerly to make the seal.
CRLaurence shows it available...they are a wholesale distributor for the glass industry and would have other supplies as well. If you can get them to sell to you. I usually can find a way to purchase from distributors or direct with a little time on the phone.
KD2037 - CRL Window Molding Clip Tool