In Win98SE (and in DOS, Win95 and WinME as well), you CANNOT change the HD drive letters. This is simply NOT POSSIBLE.
In Winnt, Win2k and WinXP, you know how this works, after the links Linney gave you.
You can either:
1. As Wolluf said, if your drive 2 contains a primary partition (easy to see with FDISK or, better, Partition Magic from Powerquest), you can transform it into NTFS. That means that this partition (and the data it contains) will become INVISIBLE and UNREACHABLE from Win98. (precisely, in the example I told you, my XP is on a NTFS partition, which is NOT a primary one, but for "confidentiality" reasons).
2. As I said, you can use only EXTENDED partitions on your drive 2: the order of the letters will be again C and D on drive 1, E and F (or more...)on drive 2.
3. The product I signalled previously, Partition Magic from Powerquest, can transform primary partitions to extended. Please note, that if you have already used XP as D: and estableshed some links, the same problem as before will happen; that the NTFS as of WinXP can only be handled with the Version 7 of¨Partition Magic (previous versions do not recognize XP NTFS partitions); and that a good backup is not superfluous before making such changes...
4. Additionally, please note that, to avoid the "links disturbances" what makes you sick, on my machines, the CD-ROM is ALWAYS M:, the recorder R: and the DVD if any is V: