It's easy!
Depending on what pedal assembly you have in your car, you might just be able to get away with this kit.
http://www2.cip1.com/ProductDetails.asp?ProductCode=VWC-113-798-901-CB
And re-use the chromed pivot that's already attached to the aluminum housing.
Or this.
http://www.thesamba.com/vw/classifieds/detail.php?id=696125
If the rearward part of the pedal assembly housing doesn't have the attachment point for the pedal pivot pin, you'll just need to grab up one of the plastic pedals with the floor hinge attached. I found one in a Super Beetle Cabrio, but they came stock in the later Beetles.
All of this is assuming that you want to retain the VW components, if you just want a gas pedal to attach to the stock Beetle cable hook-up, you can grab any of the aftermarket offerings. From Jamar to Empi, everyone makes one that will work for you.
Check TheSamba and the usual suspects listed there, you find more than you need.
Luck!
FP