I have border collies, several, in fact, and would not trust them unsupervised with the birds. I wouldn't trust them unsupervised with any sort of livestock and they all have had several years of sheepdog training and a regular herding job. My dogs are crated in the house when I am away from home, and stay in a fenced yard when they are not being worked or trained when I am home. Border collies can be a wonderful family/farm dog, or they can be your worst nightmare around kids, livestock, etc. They are very prone to developing obsessive behaviors, particularly while young, and their bad behaviors are almost impossible to break. A border collie pup is a lot of work and requires a large commitment to training. They are not easy dogs to live with.
If the OP is committed to owning one, then I would check put getting an older dog from BC rescue groups. Many can be found on petfinder.org. That way you can evaluate an adult dog to see if it fits your needs. There are also wonder BC mixes that can be found that may work out perfectly for your situation. Good luck with your search.
To Miss Fully Puffy: A border collie that is working on its own is a nuisance at best and a menace at worst. The dog that is working the guineas needs a firm correction to stop the behavior IMMEDIATELY! Do not make the mistake and allow the dog to "work" your birds, kids, etc., because it looks cute and you think the dog is getting some fulfillment out of the behavior. All herding work should be done at your request and under your command. If not, you are allowing the dog to develop bad habits that are almost impossible to break.
The suggestion to pen the dog next to the guineas would only build up frustration in the dog and be counter productive to your needs. Bambi is on the right tract; correct the dog when it is doing something inappropriate. Be firm enough to make an impression to stop that nonsense.
Good luck,
Wendy