Absolutely, total time is 20 minutes no matter what. Getting really winded is where you want to be as that is the point at which your fitness "starts" to develop. Just try to reduce it everytime you do a day 1.
Problem pullups? Got this off the crossfit website:
Jumping pullups (use as much leg push as needed, lower slowly . . . this really keeps the cardio going in a WOD like Fran)
Pure negatives (climb to top position using whatever means necessary, chair, bench, whatever, then lower slowly)
Assisted Pullups: use a Gravitron machine (if you're lucky enough to have access to one), or, even better, a human spotter to give you a lift. Bend your legs at the knees so that the tops of your feet are facing down, have the spotter support you there to provide some lift.
Assisted pullups 2: Get a large elastic band (surgical tubing works great), loop over the bar, step in it to provide some lift
Reduced load pullups: Suspend a bar (maybe an Olympic bar for weights?) at a height less than overhead . . . maybe about chest high . . . get underneath it with you legs in front and body straight . . . do "pullups" with your legs still on the ground, supporting part of your weight . .
All of these have the advantage that they are neurologically more valuable than the fairly un-natural motion of locking your knees under a pad and moving just your arms . . . in all of these, your arms are going to be drawing your whole body up . . . you will progress toward "full" pullups faster.
But yes, you can do pull-downs, and doing those are infinitely better than skipping this workout. Courtesy of Dave Wood
Personally I like body rows. Essentially you lower the bar down to midsection height, lie under the bar and grasp it like your going to bench press except there is no bench and you pull your chest to the bar. I don't have any proof but I think it develops your pullups pretty quickly.