Can anybody tell me how to make the adorable baby booties I've seen on baby shower cakes?

Do you mean cake booties or fondant booties? I have some in my gallery if they are what you mean.

To make the booties, colour some fondant to match your colour scheme, roll a long sausage shape and cut it in half so your booties end up the same size. take one half of the sausage and bend it up at one end. push a small rolling pin into the upturned part and make a hollow. pinch the edges to thin them out and give the ruffled effect. shape the toe end to be rounded and smooth with the palm of your hand. I decorated the ends of my booties with a pulled filler flower and some royal icing swirls. The laces are just done by rolling a thin length of fondant and wrapping it around the bootie sticking it on with sugar glue then adding a small bow on top to hide the join. I also made a small pink circle and put it inside the bootie so when you looked down into the bootie it looked like the base was pink.

I made my first baby boots a couple of weeks ago just to practice. I used the following tutorial:

http://community.webshots.com/album/283308759UqOctN