photoshop cs2,
i know how to convert to b& w, but not sure how to leave that bit in colour?
If you’re using the channel mixer to convert to b&w (it’s often the best way, and well worth learning how to do), you can do it as follows using an adjustment layer.
Start with your original colour photo, and add a channel mixer adjustment layer (Layer/New Adjustment Layer/Channel Mixer). In the dialog, tick the “Monochrome” box at the bottom left, and play with the sliders until you get a result you like (you can google for values which will give you the look of various film stock)
Now you can use Thorsten’s suggestion of painting in the layer mask. If you’re using the adjustment layer, you’ve already got one. On the layers palette, to the right of the adjustment layer you’ve just added, there’ll be a white rectangular thumbnail. Click on this. Nothing will change visually, but you’ve now selected the layer mask for painting. Take a black brush, and paint over bits of the image you want to appear in colour, and the mask should result in those parts from the underlying colour layer showing through. If you want a more subtle effect, reduce the opacity of the brush and build up you mask gradually