First off, grab your chosen image. I'm using a photo I took several years ago of a rose - I'm also using Photoshop CS5 but I'm pretty sure this works even in CS3.
Now, go to Image > Adjustments > Black and White. Normally I'd use a black and white gradient map to achieve a monochrome effect but this option gives more flexibility, and you can drag the sliders until you achieve your desired 'black and white'.
The image is black-and-white, so you can start introducing the colour. Go to Image > Adjustments > Colour Balance, and alter the sliders until you achieve the colour you're after.
There, done! Didn't I say it was easy?
If you've had a go, post a link to the results in the comments so I can have a look!