U-shaped bulbs have nice square fixtures, but are fairly expensive to buy replacements for. However, if they're rated for a 120 line, you can just connect them up to a standard three-prong cord and plug them into your wall (provided you have 120 lines in your home, like most of us do - just don't get a strange plug and put it in your 220 heavy appliance outlet. Come to think of it, read up on home electrical work before doing anything like this.)
I'd go with the four-foot fixtures, and see if you can't figure out what wattage they're rated for. If they're too big now, they won't be much longer, the way most of our collections go. Besides, the excess light on either end of the fixture will still be beneficial to your plants. For the price you would spend on a setup for two foot lights you could buy or build a rack big enough to accommodate those free fixtures.
They may be able to take 40W bulbs; just because they had 32W bulbs it doesn't mean they can't take higher. Many businesses buy 32W bulbs because they are a little cheaper to buy and run, and only a little dimmer to the human eye. You should be able to tell by looking at the ballast (usually a big black box with a very detailed label) which is wired between the light bulbs and the wires running to the wall. The ballast should be labeled with a range of operating tolerances, including the maximum wattage it's designed to put out. Or you can call the manufacturer, or ask your client.
Anyways, you're one lucky guy to have all those fixtures for free. This might be a good time to build yourself a grow rack. I bet you could get a few good trades on the trading forum if you grabbed some extras.
Have fun,
~Joe