Yes Wendy, just as you can paint over any other painted walls.
You can paint with an oil based paint directly over the lead based paint (which will certainly be an oil based paint).
If you want to use a latex over it, then you must first use a "super adherent primer", made by most of the paint companies now, that will allow the latex to stick properly to the oil paint. Lead is not an issue of other paint sticking. You might want to check out to know if it is a Latex or Oil paint -- and by the way, there was never any lead in latex paints.
As for the health aspects of lead paint, it is in fact recommended that you paint over it rather than trying to remove it, that is called "encapsulation". If you must remove it, do not sand it and make as little dust as possible. It is not harmful to touch, but it is harmful to inhale, or have little kids chew on it.
If you use paint stripper, collect the mess and dispose of it as hazardous waste to avoid having it go through the garbage collection centre into the water table.
If you want to know if you have lead in your paint or not, you can get a simple swab tester kit from some paint stores or off the web -- but both the US EPA and Canadian Health canada do not recommend these kits. As the Canadian bulliten says: "Since the test kits indicate the presence of lead by a colour change, the results may be affected by pigments present in the tested product. Also, the test kit may not detect lead in a product which has a protecive or decorative coating. The test results are hard to interpret since a positive reading does not necessarily mean that there is enough lead in the product to create an exposure risk. The kits have a limited shelf life, and performance can be affected by the age of the kits. Because of these concerns, Health Canada does not recommend the use of home lead test kits by consumers."
So you are left with locating a local testing labatory which could undertake a professional test to let you know if there is or is not a problem. Check with your local health authorities for a list of hazardous materials testing labatories.