Hi G S S,
Thank you for using our services.
Sitefinity is used to manage CMS pages that have been created through the CMS - either from its API or from its GUI. It does not "pick up" existing aspx pages. What Sitefinity does is to store those pages in its DB and then render them as normal pages - having all the elements. For pages that you can not recreate as CMS pages you can include them to your Sitemap as External Pages - however this will limit you to only be able to set permissions for those pages from the CMS, you can not manage anything else for external pages.
The only system requirements for your development environment would be the same as the ones that you need to run Sitefintiy - check them on this page - Sitefinity System Requirements
. The set up of the development environment can be done the same way as on any other environment. Please take a look at the following installation guide to see how to set up Sitefinity - Bullet Proof Guide to Installing Sitefinity 3.x
If you have more questions, please feel free to contact Telerik Support or post in our forums.
the Telerik team