How do you access the NXT testnet to test out new features of the system?
Download the latest NXT, and goto your conf folder and there is a nxt configuration file there. Open it with a text editor and find the line that mentions "testnet = false" - Change that false to true and then launch the NXT application. (run.bat on windows) Once its booted up you'll see in "NXT server started" message. Then you goto:

http://localhost:6876

NXT testnet is port: 6876