if the partitions are empty then this will work but it might not be the best way to doit:

as root and from a console CLI and with the partitions mounted:

chmod 777 /mnt/hda1
chmod 777 /mnt/hda3

note: 777 sets Read, Write, Execute permissions for User, Group, All

But a better way to do it and if you already have a bunch of directories and files on the partitions could be to create a new group( Music ), and add all your users to that group and then change the group setting to all directories and files on those partitions to the new "Music" group.

KUser will let you add groups and add users to that group.
chown -R :Music /mnt/hda1
chown -R :Music /mnt/hda3

If somebody knows KDE/etc better and knows of a graphical way to do this, please "chime" in since this is probably going to be a fairly common thing for home admins to want to do.