Start by checking the jumper settings on both drives.
One (C:) should be set to Master W/Slave present.
The other (D:) should be set to Slave.
Some IDE cables are cable-select type cables. On these, the connector that is plugged into the drive determines which is master and which is slave.
Next, is the second drive partitioned?
Windows will not assign a drive letter until the drive has been partitioned.
When running fdisk with 2 drives present, you need to use the option to change which drive is being setup.
Finally, some drive brands still do not "play well together" on the same IDE cable.
Some demand to be the Master drive.
Other combinations may never work.
I almost always use only drives from the same manufacture on a common IDE cable.
1 final note:
Unless you are using Windows XP, use caution when partitioning the second drive.
If both drives have extended partitions and logical drives, the default Windows drive letter assignments may surprise you.
For 2 drives with 1 logical drive on each, the letter assignments are as follows:
C: Primary DOS partition on Master drive.
D: Primary DOS partition on Slave drive.
E: Logical drive on Master drive
F: Logical drive on Slave drive.
A good article on partition strategy is posted at www.aumha.org
Chas