Only in here mind

So we've finally had our gym sorted and kitted out at work, we've got a cross trainer, excersice bike and multigym (among other things). And seeing as since I've been working in a office enviroment I've shall we say added a few Lbs!!

So now's the time to sort it!

Started this week by hitting the bike for 30-40mins and 10-15mins on the crosstrainer, want to concerntrate on cardio fittness first, then after a couple of month hit the weights as well.

I'm 30, weigh 19st 4 and am about 6ft 3, been setting the polar heart monitor to around 155-160 while on the bike, but whats the best way to work out your optimum fat burning rate and cardio rate?!?

Anybody shed any light, or offer any opinions?!?

Thanks in advance

Jason