I live in Southern California, where the temps often get up over 100 degrees in the summer. So I know a little bit about hot weather.
Here' some of the things I do to try to beat the heat inside:
*Try drinking some icy cold water before and during your work-out. It always perks me up when I feel like I'm wilting.
*I have two cheapie box fans set up across from each other, and I angle them so that I am in their cross-wind when they're on.
*If you have central A/C, turn the thermostat down low just for the duration of your work-out.
And the most unpopular advice I have: just grit your teeth and get through it, because you know it'll be over soon and then you can put your head in the freezer or jump into a cold shower for some relief.