I'd personally think that training your abs by doing situps, which is an endurance training, by just doing situps you don't actually get abs, (well you might.. but that's a whole different story). considering your back and abs decide things over your entire body.. if you know what I mean.. ever tried getting out of bed with muscle ache in your stomach?
and, you could buy some gym lessons from an official bussines thingy, ('less mills' for example), and do the lessons at home instead of at the gym.
not really sure what else you could do at the moment.. why can't you go outside? (if you don't mind me asking)
