I'd approach it pretty much like this:

• Take photo's of wooden floors, particularly try 'n get shots of one or more planks. The result will be best if the photo's are taken from as much a perfect top-view as possible.
• Then cut out the planks in photoshop or a similar app.
• Next use the transform tool to transform the cutouts to rectangles each of the same size.
• Arrange the planks in a tilable pattern, the more planks u have the more visual variation your texture will have.
• If you want tho emphasize curvature of planks or such (like on old floors) you can do this by overlaying some gradients to darken the planks towards the edges a little etc.
• Make darker lines between the planks, but make sure not to overdo it. This will divide the planks a bit more visually if neccesary. If your program supports it try and make these darker lines in a seperate layer so you can re-use it easily in specular and/or bumpmaps.
• You can tweak the colortone of the planks with some filters and such as u see fit.

The result will be your basic color texture map!

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