First check which kernel you're running:
markus@mrk-fujibox:~$ uname -r
2.6.9-301004

##### For 2.6.x kernels:

Check the append line for the kernel in /etc/lilo.conf:
image=/boot/vmlinuz-2.6.9-301004
label="Linux-2.6.9"
append="ramdisk_size=100000 lang=us hda=scsi hdb=scsi nomce "
read-only

I have 2 hd's so I need hda and hdb=scsi, delete the ones for your cd/dvd-drives, I deleted hdc=scsi and hdd=scsi.
If you change lilo.conf you need to run lilo -v to update it.

If you use grub you edit the kernel line in /boot/grub/menu.lst instead.

Then check dmesg to see where the drives are attached to:
markus@mrk-fujibox:~$ dmesg |grep CD
hdc: TDK CDRW241040B, ATAPI CD/DVD-ROM drive
hdd: HL-DT-ST DVDRAM GSA-4163B, ATAPI CD/DVD-ROM drive
hdc: ATAPI 40X CD-ROM CD-R/RW drive, 2048kB Cache, UDMA(33)
Uniform CD-ROM driver Revision: 3.20
hdd: ATAPI 40X DVD-ROM DVD-R-RAM CD-R/RW drive, 2048kB Cache, UDMA(33)

They're attached to hdc and hdd.
markus@mrk-fujibox:~$ ll /dev/hd[cd]
brw-rw---- 1 root cdrom 22, 0 Nov 14 2003 /dev/hdc
brw-rw---- 1 root cdrom 22, 64 Nov 14 2003 /dev/hdd

If needed do:
root@mrk-fujibox:/# chmod 660 /dev/hd[cd]
root@mrk-fujibox:/# chgrp cdrom /dev/hd[cd]

Now you need make /dev/cdrom and /dev/dvd point to hdc and hdd:
root@mrk-fujibox:/# rm -rf /dev/cdrom /dev/dvd
root@mrk-fujibox:/# ln -s /dev/hdc /dev/cdrom
root@mrk-fujibox:/# ln -s /dev/hdd /dev/dvd
root@mrk-fujibox:/# chgrp cdrom /dev/cdrom /dev/dvd
markus@mrk-fujibox:~$ ll /dev/cdrom /dev/dvd
lrwxrwxrwx 1 root cdrom 8 Sep 21 23:06 /dev/cdrom -> /dev/hdc
lrwxrwxrwx 1 root cdrom 8 Sep 21 23:07 /dev/dvd -> /dev/hdd


##### For 2.4.x kernels:

Check the append line for the kernel in /etc/lilo.conf:
image=/boot/vmlinuz-2.4.26
label="Linux-2.4.26"
append="ramdisk_size=100000 lang=us hda=scsi hdb=scsi hdc=scsi hdd=scsi nomce "
read-only
The append line in /etc/lilo.conf should include hdc=scsi and hdd=scsi if those are your cd/dvd-drives.
If you change lilo.conf you need to run lilo -v to update it.

Then check dmesg to see where the drives are attached to:
markus@mrk-fujibox:~$ dmesg|grep CD
hdc: TDK CDRW241040B, ATAPI CD/DVD-ROM drive
hdd: LG DVD-ROM DRD-8160B, ATAPI CD/DVD-ROM drive
Vendor: TDK Model: CDRW241040B Rev: 57S2
Type: CD-ROM ANSI SCSI revision: 02
Type: CD-ROM ANSI SCSI revision: 02
Uniform CD-ROM driver Revision: 3.20
Attached scsi CD-ROM sr0 at scsi0, channel 0, id 0, lun 0
Attached scsi CD-ROM sr1 at scsi1, channel 0, id 0, lun 0

They're attached to sr0 and sr1 which point to scd0 and scd1:
markus@mrk-fujibox:~$ ll /dev/sr[01] /dev/scd[01]
brw-rw---- 1 root cdrom 11, 0 Nov 14 2003 /dev/scd0
brw-rw---- 1 root cdrom 11, 1 Nov 14 2003 /dev/scd1
lrwxrwxrwx 1 root cdrom 4 Apr 28 2004 /dev/sr0 -> scd0
lrwxrwxrwx 1 root cdrom 4 Apr 28 2004 /dev/sr1 -> scd1
If needed do:
root@mrk-fujibox:/# chgrp cdrom /dev/scd[01]

You can make /dev/cdrom and /dev/dvd point to scd0 and scd1:
rm -rf /dev/cdrom /dev/dvd
ln -s /dev/scd0 /dev/cdrom
ln -s /dev/scd1 /dev/dvd
chgrp cdrom /dev/cdrom /dev/dvd
markus@mrk-fujibox:/$ ll /dev/cdrom /dev/dvd
lrwxrwxrwx 1 root cdrom 9 Apr 28 19:58 /dev/cdrom -> /dev/scd0
lrwxrwxrwx 1 root cdrom 9 Aug 10 13:39 /dev/dvd -> /dev/scd1


##### For both kernels:

You should have lines like these in /etc/fstab, edit if needed:
/dev/cdrom /cdrom iso9660 defaults,ro,users,noexec,noauto 0 0
/dev/dvd /dvd udf,iso9660 defaults,ro,users,noexec,noauto 0 0

Then check your mountpoints:
markus@mrk-fujibox:~$ ll -d /cdrom /dvd
drwxrwx--- 2 root cdrom 4096 Sep 5 14:35 /cdrom
drwxrwx--- 2 root cdrom 4096 Aug 10 13:23 /dvd
If needed do
root@mrk-fujibox:/# mkdir /cdrom /dvd
root@mrk-fujibox:/# chgrp cdrom /cdrom /dvd
root@mrk-fujibox:/# chmod 770 /cdrom /dvd

And check that your user is in the group cdrom:
markus@mrk-fujibox:/$ groups
markus dialout fax voice cdrom floppy audio dip src video games users usb scanner
If needed do:
root@mrk-fujibox:/# adduser your_username cdrom

If the desktop icons aren't working you can delete them and create new ones or do:
- right-click the icon
- Properties
- Device
- choose /dev/cdrom or /dev/dvd
- click OK