Your shooting - is it at the tradeshow that you need to shoot or an event prior to the tradeshow?
If so, I would forego using the iPad and use a DV cam, edit in imovie then output to iPad.
I'm a little confused - you mention needing the footage for Windows Movie Maker and iMovie? You can output an avi for windows use after the editing in iMovie if that fits your requirement?
It also depends on how much footage you're shooting? I'm not sure how the battery will last for recording long periods of time on the iPad. I know it's still not fantastic in lower light (like most cameras out there). But with great light and/or outside, it's a good enough camera. Although, I would still prefer the DVD camcorder route just in case the client wants a different quality output.
In any case, maybe try the iPad as a secondary camera to see how (or if) the footage is worthwhile. That way, you get to test it for next time, but you've got a proper camcorder as camera 1.
Editing in iMovie on the iPad is actually not too bad. it's obviously slower than a mac for outputting final files, but that's to be expected.