Peachtree Quantum was acquired by Sage in 1998. Since then, all the Pachtree products have been modified, upgraded and customized based on the new company. Therefore, the Peachtree Quantum is not available anymore, but there is Sage 50 Quantum Accounting. The application is working on the same principles only that it provides much more features than Peachtree Quantum did.
Additionally, the software has a license per year based, meaning that at the current price it will run you 1449 $.
You can check the official website for more information: http://www.sage.com/us/sage-50-accounting/quantum