"C:\Program Files (x86)\Bitcoin\bitcoin-qt.exe" -datadir="E:\Data\Bitcoin"
Symlinks may also be of use to you.
so that command will change the database to sit on the E: drive?
How you use it exactly depends on your exact setup, but assuming you have a Windows machine and a shortcut that points to "C:\Program Files (x86)\Bitcoin\bitcoin-qt.exe", and you want the database to reside in E:\Data\Bitcoin (or any other directory), you should:
1. Move your already existing database to E:\Data\Bitcoin.
2. Change the shortcut to point to "C:\Program Files (x86)\Bitcoin\bitcoin-qt.exe" -datadir="E:\Data\Bitcoin".