edit your /etc/fstab file to mount the drives so that users can have appropriate permissions, something like this:
/dev/hda1 /mnt/hda1 vfat umask=022,iocharset=iso8859-1,codepage=850,users 0 0
/dev/hda5 /mnt/hda5 ext3 auto,exec,users 0 0
/dev/hda7 /mnt/hda7 vfat umask=000,iocharset=iso8859-1,codepage=850,users 0 0

umask=022 gives read only to eveybody
umask=000 gives read/write to everybody

see man fstab for more details.