"Weeds" are simply plants you do not want growing where you do not want them and many are wild flowers that readily self seed and can be spread by birds. To keep this unwanted plant growth out of you lawn you need to grow a vigorous and healthy turf that is thick so any "weed" seeds that may get there cannot find the conditions they need to germinate. Mow the grass as high as possible which will aid in shading the soil so any "weed" seeds there do not get access to sunlight. Water when necessary, there are indications that the short time daily watering is more conducive to "weed" seeds germinating then watering only as needed would be.

Thanks kimmsr. My only problem is on the property line. The lawn itself is pretty good. We do have occasional weeds somewhere in the middle but we can live with that. Been reading some of the discussions (gardenweb) with regards to weed suppression so we may use cardboard/newspaper for a while. Followed by some ground covers later on. Thanks a lot.

You can try using Corn Gluten Meal in the spring before the weeds come up. It naturally prevents the growth of many common lawn weeds.