vista wireless laptop and wii

hi all need some help configuring my dlink524 router, it is connected
to a cable modem )low high speed)..ethernet cable ,,, running to vista
desktop (main computer), also cable running to old xp home premium
desktop which hasnt been able to connect. In another room is a
wireless wii gaming system,,, and upstairs is a laptop xp home
premium. The connection has been intermittent and unstable, so had the
cables all replaced and a new updated box (outside). The connection
stays put for a while then unconnects.. there is either a very weak
signal coming thru or not at all. I realize that the strength
varies... but the three systems were running somewhat. THe modem and
everything was unplugged, and a direct connection was made for awhile.
Now I am having trouble again , configuring the router back to what it
was so at least 3 of the connections can be fixed. Can anyone plze
tell me how to go thru this step by step in order to set the system up
so ... the wii recognizes the connection, the vista stays online,,,,
and the wireless laptop upstairs can really be wireless and not have
cables running up the walls,,,, constantly getting plugged and
unplugged thanks for your help.........and what to do to set up a
protevted wep encription from the vista... so the other two can pick
up the signal... and not someone from outside //much appreciated Vid