Hello johner and welcome to the forums.....................
What I would do is hook up the 80 gig a master on the primary IDE port.
Then hook up the 40 gig as master on the secondary IDE port.
Make sure you remove all the jumpers off of the drives.
Boot to the floppy that came with the new hard drive and it should give you the option to copy drive D to drive C. Just make sure you use the full partition size of your drive.
After doing this remove the 40 and see if it boots to the 80 and all your files are there.
Now installing the 40 back in as a slave to the 80 will require the use of the jumpers.
Depending on whether you used FAT32 or NTFS will determine how you will set up the slave drive.
What I would do is hook up the 80 gig a master on the primary IDE port.
Then hook up the 40 gig as master on the secondary IDE port.
Make sure you remove all the jumpers off of the drives.
Boot to the floppy that came with the new hard drive and it should give you the option to copy drive D to drive C. Just make sure you use the full partition size of your drive.
After doing this remove the 40 and see if it boots to the 80 and all your files are there.
Now installing the 40 back in as a slave to the 80 will require the use of the jumpers.
Depending on whether you used FAT32 or NTFS will determine how you will set up the slave drive.