MapSource

Mapsource on the web is an update version. You need to have the maps which are included with some GPSr units that don't have all of the maps (so you use Mapsource to upload them as needed), but not with those units that have the complete map set. When you get the Mapsource product from Garmin, you will have Mapsource and the Maps. You will need your unlock code (included with your c530 purchase) to unlock City Navigator Maps.

You need to purchase and install MapSource from Garmin. By the way, you can find it on ebay much cheaper than the retail price.

In most cases, if you have a GPSr with all the maps preloaded (came without Mapsource) you can get the copy free of charge from Garmin. Generally explain that you want to move waypoints into and out of your GPSr. Do a search on this site for Mapsource for more discussion threads.

How often should one update their maps for the GPS.
I have a StreetPilot i5 with Maps as of April 2006.

Should I update every couple of years? Is there a recommended approach?

You probably have the most current maps. Just like any other maps, it depends on how well they are working out for you. If you don't have a lot of new roads in your area, or the areas you travel to, you can probably wait. In my area there are a lot of new highways going in and also new developments. When the next version comes out (Sept?) I will go on the website and see if the areas I need have been updated. Depending on the answer, I will decide whether to purchase that version. Probably get one this year and then skip a year.
Remember when we had paper maps! How often did you change out your maps. I used the state maps for several years. If I bought a local atlas and the roads in the area had changed, or I ran into situations where roads I was looking for were not on the map, I would buy a new atlas.