Here's a how-to on beauty rings and moonies with a couple of photos. These are stock Newbeetle wheels, but they look quite similar to the xB.   Not mine, I lifted all this from newbeetle.org

http://newbeetle.org/forums/showthread.php?t=891

and source for parts:

http://www.wolfsburgwest.com

Parts and tool list and instructions
german hubcap clips (4 per wheel)

stainless steel 3/16" allen head cap screws with nylock lock nuts nuts on outside

line the first bend in the hubcap clip after the hole up to the ridge in your 16" NB steelie.

center punch

1/8" drill bit (sharp & slow with oil) Have a spare bit or two. the wheels are tough.

the centercaps that look like frisbees are the easiest to find and to clip on.

you can get all but the screws & nuts from wolfsburgwest.com

I got my beauty rings from my local hubcap store www.hubcapannie.com they are 16" chromes plastic and held up nicely.

Good luck!