In the source Outlook Express, create a new folder with a specific name. Do a find / search on your hard drive after that name.Check what version of OE you used on the old PC.
Create the new account on the new PC or use an existing one.
For OE5.5 you will find files *.idx, *.mdx and *.dbx.
Move these files tou the new PC.
Do a file/import/messages in the new OE, choose the right OE version.
All mails are now imported to the new OE.