From the old computer , did you go the location that is given in the "Store folder" and copied inbox.dbx or which dbx file did you get ?
In the new computer , open OE. go to tools --> options --> maintainence and look for store folder. Check the path.
go to that path and paste the inbox.dbx or any dbx that you got in that floppy (which you had got from old computer). If you have got anything other inbox.dbx, outbox or sent items then the corresponding folder name should be there in OE.
For example, if you are transferring a.dbx from old computer , then go to the folders in new computer's OE and create a folder A under inbox.
If that doesn’t help then try extract .dbx files via OE-Mail Recovery. This will allow you to easily and quickly export the files right where you need to be.