Personally, I wouldn't tow much more than a jon boat with a front wheel drive vehicle. Having the drive wheels at the opposite end from the tongue weight and where you need the most traction puts you at a disadvantage from the start.
I would guess that tops with a Windstar would be somewhere around 1500 lbs total on a proper hitch. They also do not handle much tongue weight either.
My '94 2.3L four cylinder Ranger does fine with most any trailer, my only concern with that would be traction on a steep or slippery ramp with a heavier boat. I've towed as large as a 24' Welcraft with it which weighed in at about 4100 lbs or so. It did ok, I could have used a heavier truck, but it did the job and I didn't feel at any point that I was overworking the truck or unsafe. The most I towed all time with that truck was a steel 16' tandem axle open car trailer with an E150 conversion van on it for about 80 miles, it did fine but it was slow going. The Ranger has a class IV frame hitch and is wired for any trailer I may need to tow. On heavier trailers I always use a weight distributing hitch. It's not my tow vehicle of choice, but it gets the job done when needed. I also have a one ton Dodge van, it does fine on the road, but is pretty lame on slick surfaces. It gets stuck on wet grass, literally. It's also got a full tow package and is set up with a highly modified trans and a huge cooler, along with a class V hitch. Again, it wasn't my first choice in a tow vehicle, but since I already had the van, I set it up to do the job at hand.
