My preference would be PHP over ASP for a couple or reasons.
PHP has a thriving community with tons of help available via forums such as this and PHP Builder. There doesn't seem to be as much for ASP as far as resources (others may disagree).
It is easier to find hosting for PHP and well, Microsoft sucks (again, others may disagree).
I also like Java.
As far as eCommerce go I'd look at existing solutions that could be customized before starting my own from scratch.
Just my thoughts.
-Erik