can i switch drive letters or somthing? (C:) (D:)?

[sbcirclepants]

when i formated my hdd, i installed windows on the wrong partition (c) and everything wants to install in c becuz it is default, however, i set it to have 3 gb space in that partition, and u know that that got filled up quick when i installed some progs.....so I wanna change somthing to make stuff install in drive d
....any ideas besides telling me im stupid?