I'm not confident that it will work. Speaking as someone who organized several competitions with CASH awards in this community. Check FBGD past competitions here:
http://games.freebasic.net/competitions.phpAnother one is planned soon.
I would recommend that you run it parallel in both forums, though. Nobody will mind.
I'm just not sure what sort of response you will get as this is not a prolific game making community. This would work better in some community based on a game maker (like Multi Media Fusion communities), or on some popular indie game dev site. I just don't think we have a critical amount of game developers (at this point of time) for these sort of short competitions to work. We are simply not a rapid game developing type of crowd. But this is only guessing, as I never tried. I only know that with competitions that I let run for usually two months, the community had difficulties producing more that 3 valid entries.
What I can say is that a lot of programmers in our community like programming challenges and toy-like programs (over complete games), so if you go in that direction, you might get a good response, but I doubt you will get many games with external graphics or proper presentation produced (in a mere week time).
Try, if you really have an interesting theme, advertise in both forums, but don't expect much.
Personally, I would recommend getting know with the rhythm/feel of the community first, maybe participate in my upcoming competition, before trying to organize something yourself.