The "75 watts" on that fixture is their claim about the light output of the fixture in comparison to an incandescent light bulb. The 17 watt fluorescent, in other words, puts out just as much light as a 75 watt incandescent. The "watts per gallon" rule for aquarium lighting is really based on normal output fluorescent lighting, and not at all on incandescent lights. So, you don't have 75 watts worth of light, you have 17 watts worth of light, which is definitely in the low lighting range. Sorry to say, but the light you bought is no better than the fixture you already had.
If you're looking to upgrade your lighting to something in the medium to high light range, you could go down two routes:
1) You could buy a purpose-built light fixture, like this one:
Aquarium Lighting for Freshwater and Reef Systems: Nova Extreme Compact SLR T-5 Fixtures
(you'd want the 30" Freshwater)
Or this one:
Compact Fluorescent Aquarium Lighting: Single Satellite Compact Fluorescent Fixtures
(again, you'd want the 30" light, but it comes with a 50/50 bulb for saltwater so you'd want to ask them to swap it out for a freshwater bulb or purchase a freshwater bulb like this one: Aquarium Lighting: Current Compact Fluorescent Square Pin Bulbs
in Daylight or Dual Daylight)
2) Make or buy a wooden canopy for the tank, and install DIY lighting by using a shop light from Home Depot. The problem with this, other than it just being more work than buying a fixture, is that it can be difficult to find shop lights with more than one tube that are shorter than 48".