Trouble connecting to Lynksys Router with Macbook/Windows 7

[bowener]

I am using a windows 7 laptop, my girlfriend is using a macbook, and our roommate is using a windows 7 laptop, however we are having massive troubles connecting to the same linksys router (older one... possibly the problem?). Router MODEL NUMBER IS [BEFW11S4 VER.4].

What keeps happening is that either the two laptops can connect with little trouble and the macbook cannot connect at all or sometimes it works perfectly and we can all connect or the macbook can connect and nothing else can connect.

Just a minute ago the macbook was connected, I jumped on and couldn't connect, so I plugged directly into the router, opened the router menu (192.168.1.1) didn't change anything, just saved "new" settings, and it let me connect. However, the macbook brought up a message that said another device is now using your IP address. It seems like the router is having trouble automatically assigning new/different IP addresses to each newly connected device (its set to auto).

I know some simple things, but this is just pissing me off and irritating. I have little working knowledge of Macs as well, other than that I grow increasing annoyed with trying to find anything on them.

For the love of God, and the death of Cassel, please help me! You are my only hope.

EDIT: Switched out the router for another. Possibly solved.