As usual with Photoshop and other advanced image editing programs there are several ways to correct colour balance. We'll look at the two most effective ways. The first is to use the simple Colour Balance tool. You'll find this in the Image menu under Adjustments. There is a similar tool in Paint Shop Pro X2, located in the Adjust menu under Colour, then Red/Green/Blue. For both Photoshop and Paint Shop Pro users, a more sophisticated method is to use an Adjustment Layer. The method is exactly the same, but if you want to make any further adjustments to the image you will still have the ability to change the colour balance settings later.
The colour balance tool has three sliders which can be used to adjust the relative levels of Cyan/Red, Magenta/Green and Yellow/Blue in the image, with different settings available for the mid-tones, shadows and highlights.
Since colour casts vary depending upon the lighting conditions, adjusting to correct them is more of an art than a science. However knowing a bit about the colours of various light sources is a good starting point. Compared to normal daylight, incandescent tungsten lights (such as normal domestic lightbulbs) emit a "warm" light, with a lot of orange and yellow, so to correct the resulting tint we need to reduce the amount of red and green, and add blue. Fluorescent lights tend to produce a greenish tint, although different types vary. To correct this we'd need to reduce green and yellow, and add red, but for know we'll just look at correcting the tungsten balance.
Starting with the mid-tone setting, move the Cyan/Red slider quite along way over to the left, towards Cyan. If you've got the preview button checked you'll see the drastic change in colour this produces in your image. Next, move the Magenta/Green slider over to the left, but only about 1/5th as much as the Cyan/Red one. Finally, move the Yellow/Blue slider to the right, by about half as much as you moved the Cyan/Red slider. These are only starting positions, and you'll need to play around with the settings to see what works best for your particular photo.
Next, do basically the same thing again but with first the highlight and then the shadow buttons selected. You won't need to move the sliders as far this time, but you should try to keep the same diagonal line formation.
With some experimenting you should be able to reach a good approximation of the correct white balance using this method. However there is a more accurate and effective method.