1-start with the frames that correspond to the beginning, middle, and end, of the loop (so the beginning and end of every step). these will always be whole numbers--unless you made a mistake. first, match the pose of your model with the corresponding snapshot from the sequence. be as precise as possible. then place them in the correct position (the boxes come in handy here: you don't want either foot going into either box wilst they are still on the ground. the boxes represent toe to heel distance).
2-do the same for the whole number frames that aren't at the beginning and end of the step. note that I only have one step represented. that is fine, as one can just reverse which joints to bend, and still keep it corresponding to the picture.
3-now for the ones with half in them, you have two solutions:
a. some of you may want to change the frame rate in the time configuration button from the default 30, to 60, and work steps 1 and 2 with that, and then add the "trouble" frames in (which would now be whole numbers), after which you reset the frame rate to the default (30 fps). this would split the ones that would normally be with a half, into two separate frames (in theory at least--worked for me elsewhere).
b. the other solution--the one I went with--is to omit them unless it is necessary (to make the walk more natural), at which point I would round the frames up or down to the nearest integer (alternate them), and hope for the best. As it happened, I didn't need them, so I'm not too worried.
4-export the animation, and get it into the game.