don't know the site you are referring to, but i've made my own crests for hockey jerseys that i have sewn on jerseys.
to make the crests, all you need is a sewing machine that has zig-zag (and of course thread and a bobbin), a machine needle for heavier material, and tackle twill material (the material that is generally used for sewn on hockey numbers). i have bought mine from the seamstress that does the numbers for all the local hockey shops, but am also looking at getting some from
www.jetcuts.com
the tackle twill has an adhesive glue on back that will temporarily hold it to the jerseys and other tackle twill. ironing it on will hold it on somewhat, but if you know a business that has a heat press for the vinyl heat seam numbers that will hold it better for sewing it on.
here's an example of one i did that has the german eagle (others examples are on webshots)
a friend of mine went to a local t-shirt shop that does sublimation and had him sublimate the logo of some finnish team with a weasel crest on a blank white jersey. you could also check into something like that. (sublimation doesn't fade and flake off like screenprinting can).