Swapping colours in a logo

I have an logo that has a brown background and a white foreground. How do I swap around the colours so that the background becomes white and the foreground becomes brown? Also is it possible to replace one colour with another colour. I am currently using Photoshop 6.

Thanks for your help.

Play around with the Replace Color tool, found under Image->Adjust->Replace Color. You might have to add different colors in with the eyedropper tool with a + to get the anti aliasing right. (The eyedropper + will add more than one color to transform)