A lot of times, the OS will be installed with what you need already.

When you install TCP/IP for whatever adapter... ethernet or dialup... the files are most likely already on the PC.

The OS will automatically default to "insert Win98 in cdrom" or something of that nature.
That would be too easy... for someone who has the disk...

Point the OS to the following locations... It has worked for me numberous times.

c:\windows
c:\windows\system
c:\windows\system32

all of the files should be in those locations. If not, it will ask you for the location of the next file. Simply use the find feature in explorer and search your HD for the file it wants and point it in that direction. If I remember correctly, you will have to change locations just a few times.

Some manufacturers leave the cabs on the system too. They could be in a few locations...
Sometimes they are in

c:\cabs
c:\drivers\cabs
c:\windows\cabs

You can also use the search feature for the cabs directory.

If you find someone with the 98disk, make sure it is the correct edition. Most ship with Second Edition, but not all. If you right click on My Computer and goto properties, it should show you which version you are using.

Good luck! Hope that helps!