Select the image on the canvas.
In the Property inspector, click the + sign to add a Live filter.
Choose Adjust Color > Hue/Saturation
Enable the Colorize checkbox
Set the Hue to 120, Saturation to 45 or to taste.
First, turn your image into a monochrome image. Go to Filters > Adjust Color > Hue/Saturation and set the saturation down to the far left.
Next, you want to add a color. Go back to the Hue/Saturation dialog. Set the Saturation above 0 (maybe start with 50) and move the Hue to about 90 to start with. Move the hue slider back and forth till you get the color you want. Move the saturation slider back and forth until you get the intensity you want (higher is more intense and vivid, lower is more subtle and grey).
Edit: Jim beat me again! Multiple ways of doing something! Ah...my CS3 doesn't have Jim's method, though.
Really? I was sure CS3 has this feature. It might be called Live Effects rather than Live Filters . . .
With the image selected, click on the live filters button [+] in the Property Inspector and choose Hue/Saturation. Click the Colorize box. Move the Hue and saturation sliders until you get the color you want.
Those are PS Live Effects. You want the Native FW Live Filters. Just click on that + sign in the P.I. and choose Adjust Color. Hue/Saturation is right there.
I've managed to do it, thank you everyone!