I happened to catch the last bits of a home-improvement show last night that I thought might be useful to some people out there.  The show featured a homeowner with an older toilet (3.5 gallon per flush) and the fix-it people retrofitted a newer flush and fill valve to the older toilet.  The result was a toilet with two buttons — one for liquid (1 gallon per flush) and one for solid (3 gallons per flush, if I recall correctly). I thought it was a nifty idea to re-use an existing toilet, but to conserve water (at least for the liquid-only flushes).