First off, I would secure that thing ASAP!!! Even if you have unlimited internet, people leeching will slow your speed a lot and you also risk the security of your computer (to a small degree).
Second, you should be able to set up the password without the software and without hooking up to the router with a cable. Just try opening your internet browser then go to 192.168.0.1 which is the IP address of your router. It should take you to a webpage where you can configure stuff. For my IPTIME router, I click the button to the far right that looks like a gear (Set-Up or whatever) and translate the pages (I use Google Chrome, autotranslate for the win). Just use whatever settings are by default, usually TKIP type encryption I think, and whatever channel they recommend. Choose a name for the network if you want, put in your security key and BOOM secured.
If you ever forget your security key, you can do a hard reset on the router (hold down the reset button for about 30 seconds) and it will clear the settings back to default and you can re-secure it from the start.
Hope this helps, lemme know if you run into trouble!