Most motherboards have two primary and secondary IDE slots and the cables have two connectors. Therefore 4 IDE devices can be fitted typically 2 HDD master and slave on primary CD and DVD on secondary.
Are you using 4 devices 2HDD yes CD / dvd?
You could fit an IDE controller card giving you two more slots
Or go external USB to IDE controller (£20 + use your old drive)as per Mango Grummit.