E-commerce designers please help me out.

I have searching all over the Google regarding the issue of how to convert an PSD layout to a zencart template.lam a designer by profession and had an opportunity to work with zencart.But was disappointed due to the design restrictions on the template.The owner just wanted me to replace the existing graphics with hers.I think it took away my freedom.I was wondering how the guys in Template monster do these kind of superb design and integrate to zencart.I serached for tutorials,Zencart support forum,none had any idea.everybody works on some others template(modify).

Wish i had that skill also to do my design and impliment it on zencart.

Please any body have some knowledge about this....Please reply
any links or tutorials...much appreciated.