WPG2 Post with phpthumb

Hi,
im using wpg2 with wordpress. I include images in my posts with the wpg tag "<wpg2>USA08.02/chelli/1.jpg|500</wpg2>
If i understand right. This tags loadas the full image (3000px e.g.) ans resizes it. Is that correct?
As i have a lot of images in one post it takes quite long to load the page. I have used phpthumb (http://phpthumb.sourceforge.net/) with another gallery before and would like to aks if someone knows how to integrate ist with gallery2 and wpg2.

Which file is responsible for parsing the wpg2 tag?

Thanks
Alot