Sometimes Win98 computers can get a little bit upity if the computer trying to access it does not have a user who has "logged on". You know the silly little box that eternally appears, might be worth trying.
Other options, are the files you are trying to access in a shared folder? If not right click the folder and choose "sharing", if you want to share the whole drive right click on the drive and do the same.
Check that they are both in the same workgroup as well.
Best I can think of at the moment!