If it is, you will need to scrape off any loose paint. Next, use Bondex or Weld-Crete to coat the painted brick prior to plastering it.
Vickie, if the walls not painted, skip the above. But either way, you will need to clean and dampen your wall before applying a plaster coat. To do that:
Buy some bags of masonry cement (Type N or Type S) and mix on the 3 to 1 ratio. 3 sand to 1 cement. If you mix it in a wheelbarrow, mix no more than you can use in one hours time. Anytime you have to shake the mortar to make it plyable, you lose strength. More than twice and it's a considerable loss. You don't want any flaking.
Get yourself a hawk and a plastering trowel. Cover your floor with plastic. Start at the bottom of the wall and plaster upwards. Do it as evenly as possible. As the coat of mortar beings to set, take a house broom and brush it in a downward motion. This will take off excess mortar and give it a broomed look. However, you can be creative and finish the wall with any design you want. If it's Spanish, feather the mortar on your wall and then flaten it with your trowel. Next (if you did not use white portland cement) you can paint it with white masonry cement, or any color you desire - but: dont paint it until the wall has cured for at least 7 days. Cure it out with a fine mist water spray from a spray bottle or else dobbed on with a wet paint brush daily (twice a day preferrably). Then at the end of the curring period, paint it when it's completely dry, or leave it natural.
Vickie, if you don't think you can do the job yourself, think again. It's not that difficult. Messy, but not difficult :-)
If you need further advice, I'll be happy to coach you along. In fact, I'm working on a doctor's clinic in Bonham, Texas today. Just waiting for it to warm up enough to take a plaster coat on some arches that were in bad shape. I also do brickwork, which I prefer over plastering, but that's life. Take the jobs as they come.