There are few things in a home that you can do yourself, and interior painting is one of them. I would not suggest you fix your A/C yourself, or fix a leaking roof unless you are handy, but painting is one of the things that anyone can do, even if you are not that handy.
There are few key things to remember when painting your home - if you are reselling the home, try using neutral colors not to deter any potential Buyers. If you are planning on staying in the house for awhile, feel free to use whatever colors you desire, just keep in mind that dark colors make your space look smaller in general, and also there is a difference between a 2" sample color patch and what it looks like once it's all around you on the walls. :)
The best tool for cutting close to your ceiling is the plastic flat piece with two small rollers that Home Depot or any other hardware store sells. You simply glide it along the wall, with the two rollers touching the ceiling and it creates a perfect cut between your wall and your ceiling. You can use the same tool to paint around outlets and etc. so you shouldn't need to use a brush very often. Roll all the walls and make sure you have a plastic down on your floor because rolling tends to splatter paint around as far as 2-3 feet away from the walls.
Make it a fun project - don't be in a hurry, do one room at a time and take your time, get the whole family involved if you have one, painting could actually be a lot of fun. I normally have my wife and kids write fun things on the walls with the future color that will be painted, and take pictures of them before we go over it and paint it with the desired color. It's a lot of fun, and it does save you a ton of money.
Don't fall for the usual scam - "leave it to the professional"... There is no such thing as a professional painter, it is something you can learn in 30 minutes, unless you are planning on painting murals on your walls. :)
Here is the tool you need: