I'm with marydean on this one - get rid of the weeds, and either mulch the ground or plant a green manure like peas/lentils. I'm pretty sure my brother buys supermarket soupmix (the mixed pulses and legumes) for green mulch. That will suppress the regrowth of the weeds and improve the soil, too.

Leave the lawn until you can give it the time it needs to establish (and improve your groung with whatever it might need to give it a good start), but in the mean time, decide on an area for annual vegies, and get those seeds in! Pumpkin, watermelon, carrots all grow with not much attention at all, and the odd watering. Plant peas and beans on the wall/fence for climbing (they need to be picked about 3 times a week once they're producing)- or for pretty stuff that climbs and doesn't need much attention, sweet peas or nasturtiums.

You're so lucky to get a chance to do something with the land before you move in! Good luck, and have fun with it!