Going to give this a try

Friends of mine told me them and some other guys where going to try a sprint race in the middle of October and wanted to know if I would like to as well, I said sure why not.  I don't think any of these guys have done one before and their goal is to just finish.

I came here to look it over and I'm definitely intimidated now.  First thing I need to lose some weight, I'm 6'5 242lbs right now but I've always done sports and outdoor activities. Second is I've been sidelined for 6 weeks due to a pulled hamstring(8lbs of that 242 is from those 6 weeks of no activity), finally got back out and ran 3 miles Sunday in a disappointing 29 minutes and managed a 15 minute swim yesterday.  And third I have no bike of any kinda.

Would the smart decision be to start training and if I feel confident enough come October give it a try, or forget about the October race all together and look for something next year? Prior to the hamstring I was active everyday, either running, swimming or playing flag football so I feel somewhat confident I could manage the 500yd swim and the 3.2 miles run, I just haven't ridden a bike in years.

Any tips/ advice would be great