Art,
All good points. Most bikes today that come from overseas (IE Department store) are not chrome moly but are mild steel, thus the weight. I still have my 82 gt santa ana frame from when I raced BMX and the frame weighs just a few pounds. I also have a GT santa ana 24 cruiser built up that weighs less than my son's 20"bare GT dirt frame alone. Both are chrome moly and I'll admit the 20" took some abuse from me and has a crack where the rear tubes for the rear triangle meet the seat tube(I think this came about from using z rims and tacoing the snot out of them doing kick outs into garbage cans ). the 24" still gets jumped off curbs and is a beast(hey Im 41, Give me a break).
The problem with conduit is its malable (SP) in that its soft and designed to bend. All great stuff for when running wire for the new washing machine or lights. for a frame even triangulating it wont keep it from tweaking even if its not abused. its very thin and hard to weld as blow through can occur due to lack of heat control from inexperienced welder. not to mention that most conduit is galvanized and is just plain nasty to weld. (don't inhale the green smoke)
Jody it sounds your going to do what you want to do. I would strongly advise against conduit and instead find a scrap steel yard and get in with proprietor and see if he'll let you dig around for cut off and drops for your needs. If that doesn't work, cut up old bikes for what you need. you can get them by the truck loads at the local police auction..