I don't know how you build your new sites but I think Paypal has prepared all scripts for any purposes. Just go do their site and find the script.
I also think zen-cart would be suitable for your purpose. It has built-in support for paypal
Hmm how you feel about joomla then? If i can suggest sth is building gallery using one of joomla's plugins for that (there are dozens of them) and integrating it with VirtueMart plugin (its ecommerce plugin for joomla). I've came across art-selling online store based on joomla and virtuemart the other day - it was working great.
If you use an offshore LLC or IBC (international business company) as your selling company then you can either set up your paypal account in the U.K. region or even Switzerland is a possibility but if you work with an Australian Bank account you will not be able to unless you are actually in Australia and have a company registered with the government there. If you are outside of the U.S. and work through a company you will have to fly to the U.S. to set up your company bank account since 911 the KYC policies are very strict. But a personal bank account in the U.S. is possible and you can set up your paypal account using your U.S. bank account which is in your personal name.
yea, the simple paypal buttons that can be configured on the paypal site, can be used on a page. You config it in paypal, then get the html, then paste. The button renders the paypal invoice for x$$$ and pays to whomever you set.