Erm.. no recommend using this way to get 6Vdc, output voltage easy to change when load parallel connect with R2.wyx said:to halve the voltage, try connect this way with R1=R2.
12Vdc --R1-------o-----6Vout
|
R2
|
Gnd
PS: connect R2 to Gnd at the mark o. I can't align the lines to its exact conenction :P
Try using LM317 - Adjustable Regulator, u can get the stable 6Vdc voltage with few passive components in circuit....
LM317 Datasheet