Hi M.,
I have refinished lots of furniture and painted almost all of the rooms in the four houses that we've owned in the last 9 yrs. There is a product available at Lowe's called Bulls Eye 1.2.3. Primer for all surfaces by Zinsser. It's great because you don't have to sand prior to painting. This stuff sticks to any surface and is easy to clean up as it's water based. It doesn't have a horrible smell like the shellac based primers either. I just used it to prime a book shelf for my daughter and I loved this product.
I think you should go for it you'll be surprised how it will change the room and you'll have the satisfaction of knowing you saved money and YOU DID IT!
First you'll want to wipe down the wall to make sure you don't have any dust or cobwebs lurking in the corners.
Second, prime the walls. The above mentioned primer dries fast so you can paint over it in an hour or so.
Lastly, paint your walls in the desired color and your done.
One tip I would like to pass on to you is the following:
If you're not painting your base boards, you'll want to tape them off using the blue painters tape. Make sure you remove after you prime and after you paint BEFORE THE PAINT DRIES. You'll get a crisper line because if you're not so neat and get alot of paint on the painters tape and let it dry, you'll pull some of the paint off the wall.
Good luck and let us know how it turns out.