This guide is written with the Photoshop user in mind but I'm sure the principles contained therein could be applied to most graphics programs.
http://www.slexchange.com/modules.php?name=Marketplace&file=item&ItemID=618515

Included in this package:
Pocket's Guide to Clothing Templates (wearable book)
*PP* Top Template (with alpha channel included) and a fabric sample to work with.
Any questions, please feel free to contact me and I'll be more than happy to help in any way I can..