TE,
http://www.gaywidewebmasters.com - plenty of resources there to get you started ...
As Nick said, we all have a 'pet niche' that we are best at, but a good marketer can sell ANY widgets to ANY audience - if its not your pet niche, you just need to spend more time researching your audience and your widget, and see what it is that brings them together.
While it is a lucrative market, you are putting yourself in a position where you are competing with sites that are of a much higher standard in general than straight porn. And if you rely on text to sell to surfers, you'll have to really learn the market well ...
The biggest mistake straight men make when trying to target the gay market is being offensive, without realizing it ...