Before you think I just posted this without looking into it, I've researched
and researched and researched via Web and a couple friend DIY'ers and a
professional, and the common fixes I've seen wouldn't work here.

Our living room floor is SUPER squeaky; a 30 lb dog will squeak as loud as a
person, and it's pretty much the WHOLE floor. Just standing in place and
adjusting your weight from toes to heel will creak the whole room, and
someone walking across it will vibrate the whole room and rattle stuff on
shelves, etc. There are also a couple places where you can see with your
eye that there's a little dip in the floor.

Now, this is a really nice old hardwood floor, with 4", 6", and 8" planks,
3/4" thick, with dowel covers that are actually real and cover where the
planks were screwed into the diagonally-running 3/4" toungue/groove
subfloor. It looks terrible (has been carpeted w/ obvious multiple spills,
etc., for decades), but I've managed to talk my fiance into letting me try
to fix the squeaks and refinish the floor (it was a tough battle).

The only fix that seems like it might solve the problem (talcum powder, etc.
will NOT solve this) suggested to me WITHOUT having to removing the floor,
replace the subfloor 3/4" toungue/groove with plywood, and then reinstall
the hardwood, was to go to the basement and screw diagonally upwards through
the joist and into the subfloor, about 2 screws for every subfloor plank.
Now, this would put a HECK of a lot of screws through the joists (the
subfloor is 9" wide planks, running diagonally to joists), and I worry about
just tearing the joists and subfloor up without actually fixing the problem.

Some things that are of interest:

- Seen from below (in the basement, looking up at the ceiling, which is the
joists and subfloor of the living room), the subfloor planks are obviously
toungue/groove, but they are spaced so it looks like the toungue wasn't
actually put INTO the groove; I can see the toungue in almost all of the
planks, so there are these little gaps between all the subfloor planks where
I can see what I assume is the toungue of each one. Maybe this is part of
the problem?

- The joists seem to be the typical 2 x 9's, and seem to be in decent shape.
There are a couple double ones (2 joists right next to each other all the
way across this span), and a couple places where a small section of joist is
right next to the full-length (I'm assuming this was done during install,
and they saw some need for additional reinformement). One thing I did
notice is that almost all of those wood X-shaped cross-supports between
joists are doing nothing, like they're all loose, or just hanging there
without being firmly nailed in to the sides of the joists.

- The majority of the creaking, if you're a complete newb like myself and
going by feel and guesses, FEELS like it's the hardwood floor itself moving
slightly. Like, I might be completely wrong, but it seems like the hardwood
floor itself is moving a tiny bit under your feet, not the hardwood floor
being firmly connected to the subfloor, and ALL of that moving. I could be
wrong, this is just a "got a feeling" thing.

So here are my options as I see them:

1) Use a screw to remove all the dowel covers (they're glued in, but I
successfully removed several of them by screwing in a screw and using the
claw of a hammer to pry them out), and tighten or re-screw the hardwood
floor into the subfloor and (if that's where the screw is) the joist below.
If this works, saw a bunch of new dowel covers and glue them in.

2) If 1 doesn't work, try this thing with screwing upwards from the
basement diagonally through the top of the joist into the subfloor.

3) If 1 and 2 don't work, try as carefully as possible to remove the
hardwood floor, replace all the subfloor with plywood (taking care of any
leveling problems as long as I'm at it), and try to reinstall the same
hardwood floor.

Are there other options, or better ways to try these options? Might it be
cheaper, or a better idea, if 1 doesn't work to get new wood milled (they
don't sell these wide planks anymore, or the dowel covered technique), or
maybe just get today's hardwood, rather than risk damaging the joists trying
to save this floor?

Any help here would be much appreciated. I hate to lose this old floor
(house built in 1929, and I'm assuming this is the original floor, and
everyone who's looked at it has said I'd be crazy to replace it), but I
don't want to screw up the joists and turn this into a complete joist
replacement as well as floor replacement, you know?

Thanks for taking the time to read this and to respond.