Easy as pie. just the two pronged stereo removal tools from halfords or somewhere like that and remove the old one. Then wire up a cd head unit in its place. Piece of pie!!
An alternative tool is two six inch u shaped bits of coat hanger with the ends cut with good pliers at 45 degrees. Can't remember if the slope is needed to present to the inside or outside of the radio, but make them opposite, and you can change which side you plug them in.
cheers
Russell [;)]