If you have a straight-through 40 pin or 80 pin cable, set the master drive to 'Master with Slave' or 'Single/Master' setting, and the slave drive to 'Slave'. This varies with the drive make.
If you have a Cable Select 40-pin cable (identified by 2 crossed over wires between the drive connectors) or 80 pin cable (usually done internally in the connectors), place the jumpers on both drives to Cable Select, and mount the primary drive on the far end connector and the slave on the middle one.
If trying the Master/Slave jumper pair doesn't seem to work, try it with Cable Select. Many times the cables are poorly marked as to what their configuration is.
Also, some drive makes have a history of not co-operating with other hard drive brands on the same cable. In this case, use the slave connection of your CDROM cable and secondary IDE channel and copy the partition over if necessary, so that your faster drive ends up as your primary master and the slower one runs as master or slave opposite the CDROM or CDRW.