1.
Step1- Goto Image>>Mode>>Grayscale
Discard all color information.
Step2- Goto Image>>Mode>>RBG Color
Step3- Goto Image>>Adjustments>>Color Balance
Step4- Adjust the sliders to desired effect.
2.
Discard Step 1 and 2 on the First way.
Steps 3&4 are the same.
as with many functions in photoshop there are quite a few ways to achieve this, the easiest is to bring up the hue/saturation panel (ctrl u on windows) and click the 'colorise' box.
you'll have more control and quality doing it wmleebo's way though, I just wanted to point out that there's always more than one way to do something in PS, that's why I love it.