Yes it is possible. On a peer to peer network. A win2k machine uses its local security database for authentication. And win2k always applies NTFS permissons or share permissions to the folder/files. And u need an account to even access microsoft networking with a win2k machine.
In simplier terms the username you use to log on to the windows 98 machine with has to have an account on the Win2k machine. And also check the NTFS and share permissions make sure that user account has access to it.
FYI. If you have setup your win98 machine so it doesnt ask you for a username, windows still uses a username. The easiest way to find out what it is, is to click on the Start Menu and next to log off it will have your win98 username.