<p>I have googled quite a bit and I cannot find the answer. So how many characters can be stored in a Windows Installer property value. If you give an answer can you provide the source of the answer?</p>

The MSDN documentation isn't very clear on this, but it does provide some hints.  For example, this article mentions that property values may be written to the registry, which means that registry value limitations apply:
http://msdn.microsoft.com/en-us/library/aa372432%28VS.85%29.aspx
Here is an article detailing registry value limitations:
http://support.microsoft.com/kb/256986
So at a maximum, I'd use the registry value limitations as a guide (and still try to stay well below that).