Guillermo,
First share your XP folder and give it a share name.
Then what you need to do is create user accounts on the XP machine for your 98 users and grant them at minimum read/write and file scan permissions (r,w,f) on the folder you want to share.
Then on the 98 machines, map a network drive to the share. To map the drive open Windows Explorer on the 98 machine. Select Tools | Map Network Drive. Leave the drive letter whatever it defaults to. That will be the first available drive letter. For the path you will type in \\machine name\share name where machine name is the computer name of your xp machine and share name is the name you just gave the share. (both are case sensitive. For example, my Windows 2000 machine (works the same as XP) is MASTER and I just created a share called ATNOPRO so I would type in \\MASTER\ATNOPRO
So you don't have to do this everytime they reboot, check the Reconnect at logon box. Click OK You may or may not be prompted for a password. If you are, then type the username and password you assigned for that user. If the user is an administrator on the XP machine and they have a user account on the 98 machine that is the same as the XP machine it probably will not need a password. If you've followed these instructions exactly, the new drive should appear as (in my case) ATNOPRO on 'MASTER' (I:) (where I: is the drive letter mine defaulted to - your's of course will most likely be different.)
For the users to access the share all the have to do is go to the mapped drive, either in My COmputer or Windows Explorer and use it just like it was their C: drive.
I promise you this works, because I've been using two 98 machines accessing my entire C: drive on my 2000 machine (and at one point when I had XP the same with that) for the last couple years. And I just did it again with a new share just to make sure I gave you the correct instructions. If you follow them exactly, I promise it will work.
Cheers
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Alexandria Networks. Leader in IT consulting for associations/non-profits, and small to medium sized businesses around the northern Virginia and Washington D.C. metro area.