Redwing, I think I know what happened. WinXX does not allow you to specify which letters go with which partitions. The letters are assigned on the fly based what the computer sees when you boot up. By adding a new drive, you've shaken things up.
I once had the same issue and found a detailed write-up on how letters are assigned, but can't find the link now. It goes something like this: The first letters are assigned to the first primary partition on each physical disk in you system. For a 2 IDE channel system, I think the order is first master, second master, first slave, second slave (could be wrong here). The next letters are assigned to the logical partitions in the virtual paritions on each drive (all logicals on first master, then all logicals on second master, etc.). Finally letters are assigned to all the remaining physical paritions on the drives.
So, in your case, the first physical partition on your orginal drive remained C:, but the first physical partition on your second drive now gets the next letter D: (and your old D: becomes E🙂. As far as I know, there's no way to overcome this.
This really sucks! And is one reason why fewer people are as partition-happy as we were back a few years ago (when my partitioning reached up to L: !!!). I believe AT has a FAQ on partitioning somewhere...
