All your IDE drives (each of 2 IDE slots on your motherboard can provide you with 2 drives - 4 IDE drives amount) are named like hd??. The first drive on the first IDE slot is hda, the second drive on the first - hdb, the second drive on the second slot - hdd. This drives can branch with numbers (e.g. hda5) what means partitions. Numbers 1-4 are for primary partitions and other for secondary. If your hard is hdb and has 2 primary and 3 secondary partitions, it'll contain hdb1, hdb2, hdb5, hdb6 and hdb7. Therefore reconnect your CD-ROM to another slot and it'll become not hdc.
Do you wanna mount hdb7 on boot? Add "auto" option to the according line in fstab in column with mount options
It's all easy