I have a problem with that old FAQ file and much prefer the description in the current v4.63 manual.pdf file of install to Memory stick as a beginning point. Keep in mind your v4.51 may have problems with newer OS machines that require v4.52 or later and really should only use v4.63.
To import old data and files you want only some files. Some others you definitely do not want to copy to the new USB stick install location like any old pmail.ini or any old pmail.cfg or pmgate.sys files plus and old user stored files that might have been stored in home mail box location of old install. You want your new USB stick install to be as clean and lean as possible due to the comparative slowness of read and write of the stick as compared to speed of a PC hard drive install.
http://www.vandenbogaerde.net/pegasusmail/pf_pmfiles.html is a very important reference to help you determine what files are and which ones you want to copy from the old install to the new USB install to have your new mail messages, message folders and address book information on the new stick.
The use of -a and -roam switches as part of command line/icon properties used to start the USB stick install of winpm-32 plus the -I <user> are very important. You may also wish to include -o to start in offline mode at first also. See either manual or Help and Commandline options information for more. When using stick install on local LAN you may need one set of settings but almost certainly also different set as either second Username or another Identity for the Tools, Internet options Receiving tabs and below and almost definitely a different set for use of the USB stick when out in the outside world across Internet connections other than home or work location that usually require different port numbers and different authentication entries. Remember that the host machine use of USB stick will provide only the basic OS and temporary files place and all other must be present on the USB stick and all file saved writes will be to the stick only.