PayPal Payments Standard w/PowerStore
That is a very good question. The answer is yes, but we would not recommend it.
If you were to change the payment gateway in PowerStore to PayPal Standard (or most other Remote Checkout options in eCart), you will lose some very useful functionality that is in PowerStore. Features such as inventory management, and order management, will stop working because of the way PayPal Standard's Remote Checkout works.
Alternatively, i would suggest that you use the PayPal Express Checkout option. It is free and already in the product - saving you from having to make any custom changes. I'd suggest running PowerStore on your live server - Use Express Checkout and see how it works. For most people, Express Checkout is the best option as it is free and you won't lose any of PowerStore's functionality that you paid for.
To sign up for Express Checkout go here: express_checkout
You can always pull down your live PowerStore and install it locally to make changes later. But at least this way, you have a working PowerStore that you can start populating with products right away.