Hi Alex,
Well, firstly, welcome to VATSIM. I'm sure you'll have a good time.
You might want to consider using VRC for observing and initial training on VATSIM. ASRC is older software compared to VRC, and generally speaking, VRC is easier to use for first-time members. ASRC is still an excellent program, but you might want to hold off on it until you're experienced enough to use it proficiently (VRC is a point-and-click-based client, while ASRC is mostly memorized dot commands).
Anyway, yes, you can still observe without having to take any exams. To do this, you'll need to have the sector file for the area in which you'd like to observe loaded in your radar client (VRC or ASRC). These can be found at the websites of each facility. If you're looking for Phoenix Sky Harbor sector files, you can find them at the Albuquerque ARTCC website,
http://www.zabartcc.org/ . A full list of VATUSA ARTCCs is available on the right hand panel of
www.vatusa.net.
Once you have the sector file loaded, you'll want to connect to the network to observe. In VRC or ASRC, go to File --> Connect, at which point a new box will appear with fields in which you can input your connection information. Use an observer callsign such as ZAB_OBS (ZAB is the three-letter identifier for the Albuquerque ARTCC, and OBS indicates that you are an observer) when connecting. Then enter your name. Select "Observer" from the facility drop-down menu and the rating drop-down menu. Then enter your VATSIM CID and password, select a server, and click connect. You'll also probably want to adjust your visibility range from the default 600 down to something around 50 miles, more or less depending on what sector file you're using. To do this in VRC, go to Settings --> General --> Airspace [tab] --> Visibility slider. To do this in ASRC, go to Settings and adjust the slider.
For more information on ASRC, visit
www.asrc.info, and for more information on VRC (including an observers' guide), go to
www.metacraft.com/vrc .