I just want to comment that THIS is the time to decide, BEFORE you put down anything toxic, whether you want to use conventional chemical herbicides, pesticides, and fertilizers, or try to stay non-toxic and organic all around, or take a middle stance.
Do read up on pro and con arguments -- look around in the Organic Gardening section and the four sub-forums therein, or use the search box available at top left of most pages.
The presence of a "weedy" lawn *to me* indicates a relatively poison-free
property with a healthy
eco-system, rather than a "neglected" one as some (or most?) may think.