My wireless router died and I had to replace it (No wired or wireless connections were working.)  I purchased a standard ‘g’ router and got everything up and running, or so I thought.  It was pretty laggy and just did not have the same speed as the last one.  I fired up my netbook and ran Wifi Radar to see what other networks were out there, and what channel they were on.  Turns out, almost the whole block is running channel number 6! I found out this is the default for wireless ‘g’ routers.  Changed the channel to channel 3 and instantly my laginess went away and my speed more than doubled.  So, the lesson learned is when setting up a new router, check to see what the neighbors are running and pick something at least 2 away from theirs.  Sadly there are only 11 channels, so in a busy apartment building, this may just be a case of trying all the channels until one works for you.