SLRs have interchangeable lenses: you take one lens off and put another on to get different angles of coverage, wider apertures, etc. Every SLR line has its own lens mount; you cannot normally swap lenses between an OM-4, a Canon EOS, a Nikon, etc., though you can swap lenses between different bodies, film or digital, within one family.
With the exception of the new E-1 (which has a new lens mount), no Olympus digital camera has interchangeable lenses. You can sometimes augment the range of a digital camera's built-in zoom by adding wide-angle or telephoto adapters, which attach in front of the lens (and which normally require lenses with threaded front elements to hold these adapters or filters). I don't know offhand if such adaptors are usable with a C740.
I assume that the "lens tube" you refer to is an extension tube, normally placed between an interchangeable lens and camera body for ultra close-up work. Without lens interchangeability, that won't work, either.