Sounds like a fun project. If you want to put a garage over that location later, you'll have to put a lot of rebar in the footings, and maybe consider putting a few piers in down to the level of the pool bottom+. (sounds like a real pain, but pretty wise)
In order to fill your pool in, you'll need to first bust up the bottom. If you don't, any moisture from rain won't get out fast enough. Might require removal of the liner a/o jackhammer use.
Depending upon your locale, most cities would require you to remove the pool prior to filling it in. If you are less concerned with the locals, you could hire a landscape contractor with a Bobcat, and order a bunch of gravel, and fill it up. I'd stronly recommend using a material that will settle nicely, and pack it well with a tamper ever 6 inches or so, perhaps sand, others will probably post. Finish with a foot of topsoil or more, than apply sod/seed.
I'd plan on paying a contractor quite a bit depending upon how much you need done, but I'm thinking in the neighborhood of 5,000. You could probably rent a Bobcat and plate tamper, and do some of the work yourself, but the sand and dirt will probably cost about a thousand bucks, and using a Bobcat in this location won't be fun, and is very, very dangerous for newbies.