Learning to do your own work can be both fun and rewarding, but you're starting from scratch on a fairly major project.
I would suggest getting a decent book, if only from the library. Zinn is good, as is Bicycling Magazine's book on bike maintenance.
If the hub bearings are shot, (quite likely on an older bike) you will most likely be able to rebuild it without springing for a new wheel. You should familiarize yourself with the correct terminology as well, it makes it easier for forum guys to give good advice.
The tire is the rubber thing on the rim. The rim is attached to the hub by spokes (usually
). Inside the hub are an axle, ball bearings, cones, and various spacers and seals. In order to dissasemble/reassemble the hub you will need to buy some "cone wrenches", very thin wrenches to hold/adjust the bearing cones.
There are also excellent online resources for all these things, including the fine Park Tool site.
Good luck!