I had a client just start complaining that when they were working in and closing Peachtree it would 'hang' their computer. After a couple hours of digging in Google and Peachtree support I came across a good post talking about how a large database could slow down Peachtree performance. I checked and they had a 60Mb database. Doesn't sound that large, but Peachtree claims you can see degraded performance with a 10Mb database. I tested my theory by opening the sample company that comes with Peachtree which was 400Kb in size. It opened and closed like a champ.
What can you do to fix it? Not much. You can close out fiscal years, but you loose all the years details. My client decided to just live with it for right now.