R2D2: Yes, it normally will change. But, the good news is you can tell the system that you want it to be a specific drive letter.
Right click My Computer
Select Properties
Click Device Manager on top tab
Click + sign on left of CDROM
Double-click your CDROM drive
Click Settings on top tab
Bottom 1/3 of screen allows you to set the drive letter.
I use this for Zip Drive and for CD.
Good Luck!