Lots of good information can be found here: http://www.epa.gov/lead/pubs/leadinfo.htm#protect
Having said all of that, around the Philly area, it is quite common to simply keep piling on surface coats of latex paint to cover over the lead and reduce the potential for dust or chipping.
The areas to worry about the most are door frames and window frames where friction from the motion of the doors and windows can create flaking or paint dust (inhaling lead is far worse than eating it, apprantly). Also, pay special attention to the children's rooms.
The real difference in lead testing is that some companies use a machine (x ray technology) that detects lead right down to the wood, even if painted over. Others use only a swab test which will identify only lead that is on the surface. If you opt for a less thorough inspection, I would say to test children's rooms first (or more throoughly) and assume that if the rest of the home was built at the same time as the kid's rooms, then similar materials were used there, too.
There are many different factors involved. First of all, assume there is lead paint and that you will need to have the place deleaded. Now, If you plan on making renovations to the property you should wait until the renovations are done before having the test done. Tearing down walls and ceilings will stir up the hidden lead paint particles and most lead paint inspectors will tell you that this is more of a problem than kids chewing on window sills.
If you don't plan on renovating, have the test done and go from there. Use this link http://webapps.ehs.state.ma.us/Leadsafehomes/default.aspx to see if there have been any previous tests done on the home. Let me know if I can be of any more help.