Connect through a wireless

Hello,
I have Siemens Gigaset SE511. When I tried to connet to my wireless device via internet browser by writing the router IP:192.168.2.1 it works and ask the password. Even at the window it says the factory set password as admin. I am writing the password and it says it is not valid. How it would be possible. And how I can set my wireless net?

I have to add that I am using Vista and Siemens doesn't provide Vista Cd for the router.

I thank you advance for all your helps...
best
sab