I have an existing site to which I would like to add shopping cart buttons, as opposed to redesigning the entire site as a store. I know I can use paypal, but I have a authorize.net account setup and would like to use that. Aren't there options that just use buttons to add to a cart, other than paypal? (Paypal has worked fine for me in the past btw - I see that there are many who have had problems with that. ) I am currently using a paypal button, but only for one item.
Is anyone familiar with cartmanager?

Here is the site I want to add to:
http://www.paintedphoto.com

Suggestions would be very much appreciated!

Thanks Julian,
I have been using paypal but now I have an authorize.net account and want to set up my own buttons, like with cartmanager...same idea as paypal.