I just went through this with my new 125g tank. I was putting it kiddy-corner to two load bearing walls (the outside corner of the house)
looking in the basement -I saw that the 2x11 support beams were running in parallel to the tank (ug!). Back upstairs, I located where along the floor the two beams were running, and moved the tank out from the wall such that the weight was evenly supported by the two beams.. (I had initially set it down closer to the wall, in which case it would have only had one support beam running down the center of the length of the tank.) Yes, this meant the tank was farther out from the wall than I wanted, but it's actually nice being able to get in behind it..
Anyway - the support beams are 16" apart from center, and the tank+stand is approx. 19" deep, so I just centered it over the two beams.
This *probably* would have been ok.. but I was looking around the local hardware store, and they have the floor jacks for $16 each, so I figured "eh, grab two, a cheap insurance policy".. I placed them in the basement, one under each beam (I think they support 14,000 lbs or such.) and placing them there gave me a great deal of comfort..
125g of water weighs approx. 1000lbs, plus the tank and stand and rocks/gravel we're looking at at least 1600lbs, over an area of ~12sq/ft.. better safe than sorry.
Also - be sure that you don't do what I did and check that the tank is level before filling it up with water.. Get some of those composite shims (sold alongside the wood shims at your local hardware store, only they are much stronger) and shim up one side as necessary so the water level is even.)