The basics you need to look for are:
You need the laptops default gateway IP address to be the IP address of the router, and the subnet mask needs to be the same (generally 255.255.255.0 and configured by DHCP - thats the automatic IP address assigning system inbuilt into most modems). Check if you can access the modem via your web browser (i.e.
http://192.168.0.1/). If you can't, then that's where your problem is (you aren't in the same IP range or subnet mask). If you can, then check that you are set to go through it, and that the modem itself can connect to the internet. If that's all fine, then download a small linux distribution, burn it to a CD (make sure the linux is a live bootable distribution), and then test if linux can use the net. If it can, then you have a software problem.
-Stephen