For starters, there's lots of free clothes to find at 'Rosity's Free Stuff.

If you're not happy with them, then I think there's a tut on painting clothes at Arcana - now run by DAZ.
Lets see ...
Ah yes :

An Excercise in Painting Clothes Using Photoshop - By Will Kramer - A detailed step by >step on painting clothes on Poser characters. The tools and techniques demonstrated here >can aid in the rendering of many types of clothing onto Poser figures.

Go to:
http://arcana.daz3d.com/tutorials/index.html

Happy painting !

--- Bakkti ---