BeckyW, you will find lots of info about geocaching at the
www.geocaching.com site. That is definitely the place to start. There is a special section for getting started (click on the link in the upper right hand section of the geocaching.com home page). Also ask any questions in the Getting Started section of their forums. People there are very knowledgable and very helpful.
As far as a choice of gps for geocaching (or for anything else!), let me recommend the site
www.gpsinformation.net It is not visually very attractive, but it is loaded with valuable information.
I have used a Garmin GPS V for years. It works well for both on road navigation and for hiking/geocaching. I have considered upgrading to one of the newer Garmin units so I could have a faster computer connection (The V uses only a serial connection rather than usb.), more memory for more maps, and possibly color, but I have been reluctant to do so because the newer units lack the ability to switch screen direction. When I have the gps mounted on the dash of the Jeep, I much prefer to have the screen in landscape mode (if that is what you call it on a gps screen
)
By the way, I don't want to get into a debate over Garmin vs Magellan or any other gps company, because it is like asking someone to pick between car companies. I can say that Garmin is an American company and it has a reputation for absolutely incomparable customer service. I can add my own testimonial about customer service. When we were getting ready to go to Big Bend NP last summer, I e-mailed Garmin to ask when the more detailed topo maps of the National Parks in the central part of the country would be available. (These are available now, but were not available at that time.) The tech responded very quickly that it would not be available for purchase for at least several more months, but he would load it onto by gps unit if I was willing to send it to him. It turns out I did not take him up on his offer due to time constraints, but I was very impressed by that.