The two posts already made, assume that there are no messages that you wish to keep, that may already be in your new PC. If this is the case, then fine. If, however, you wish to merge old with new, then a proper import is necessary.
In all probability, a floppy disk will not have enough space to perform a proper import, since you will need the file named folders.dbx in addition to the file named inbox.dbx
If you have a usb pen drive or card reader, you can create a folder named Outlook Express on the media, then copy from your old pc the files named folders.dbx and inbox.dbx to the folder you have just created. Then from Outlook Express on your new PC, select file>import>messages and from the next dialog screen select Outlook Express 6, click NEXT and check the box named 'Import mail from an OE6 store directory' and follow the instructions from there.