Accessing encrypted wireless network

Encryption problem:

I recently set up a wireless network to connect a new Sony Vaio lap top to the internet via a cable modem. The router I bought is a D-link rangebooster N 650 router.

When I set this up it was encrypted with a password. Every time I have used this link via the sony I have not had to type in the password, it has been done automatically.

I installed a D-Link USB wireless adapter (model not DWL- G122) on my old PC to enable that computer to communicate with the internet via the D-link router.

I followed the installation instructions on the CD and book supplied. It appears to have installed correctly.

I then went to connect to my router and selected my wireless network by name. I then followed the windows XP instructions for configuring to my wireless network.

When I typed in what I thought was the password into the space saying "network key"  a diologue box popped up that told me the network key was only 5 characters long and I had typed 8.

Is the "Network key" the password that I used for the router?
If it is I have forgotten my password.

Is there a way of finding out what the forgotten encryption password is, or does it have to be reset? My concern is that if the router has to be reset, I might risk losing the internet connection via the Sony Vaio and will have no internet.

Any ideas?

Thanks.

Mike Ludd