If you are installing a new hard drive to be used as a system drive...it could.
If you are installing a new drive that is just another drive...letter assignments don't matter much once you get beyond C: and D:.
The presence of a card reader should have no impact on a new system drive, since it precedes the card readers when it comes to hardware recognition. OTOH, if this hard drive has been merely added after the card reader...then it logically makes sense for letter assigned to be farther up the alphabet.
All drive letters (except C:) can be changed by using the Disk Management feature of XP.
Disk Management - http://www.theeldergeek.com/disk_management.htm