Yeah, WiFi is not the fastest. Even if you hit the theoretical maximum of 50Mbps on 'G', that equates to just about 5MB/s once packet over heads are taking into account. Then there's the fact that this is never achieved in reality, say you get half on a good day - so there's 2.5MB/s. Then there's two devices sharing that bandwidth where full duplex can't be used. Then add other wireless networks interfering on the channel etc etc and it's quite possible that 0.7MB/s is all you'll get.
Try changing channels, or even better, put in a wire connection if you can to one of them to the router, could make a difference.
Also, if I remember correctly ad hoc networks don't support MIMO, so 50Mbps would be all you're capable of getting. You can always try to move the receivers closer or try to move obstructions (big thick appliances and microwaves) out of the way. If you have an N router you'd be able to get speeds of 150+ if your computer's card can handle it. Even an inexpensive G router would likely double your current speeds. Power line adapters may increase it further.
Something close to 1-1,2MB under perfect conditions sounds about right for an ad-hoc network using 802.11g, because 802.11g does 54Mbps in infrastructure mode but only 11Mbps in adhoc mode. If you don't want a full network infrastructure (at a bare minimum that would be a switch) have u tried a crossover cable? Or at least USB-USB connection?