Win7 default user profile/permissions should be ok for c:\pmail and all files below. On all my win7 machines it was not necessary to change from default.
What would be or will be problem is if you had old setttings and preferences found. Did you use, copy, import anything from a former install or another machine with different OS version? You don't want any old pmail.cfg or any old pmail.ini file to be found but it is ok to import old data files only.
http://www.vandenbogaerde.net/pegasusmail/pf_pmfiles.html
is reference for Pegasus Mail files and locations and descriptions of function.
Was this a new clean install to the win7 machine? What is the commandline being used to start program now? Is it something like c:\pmail\programs\winpm-32 -a -roam -I Admin
where Admin is the default username created by installer.