Googling MN-500 reveals that it is a 802.11b capable wireless router (you might have mentioned that).
You should be able to set it up without any software -- just link the laptop and router via an ethernet cable and open Internet Explorer and put in the router's IP address.
The IP address of the router can be found by opening the Windows Command Prompt (Start, All Programs, Accessories, Command Prompt) and typing ipconfig /all -- this will reveal the IP address of the gateway device, hopefully your router.
It's usually something like 192.168.0.1
If that works you may be greeted by a login box -- the default Username may be admin and the default Password may be password.
If not you'll need the manual for the router.
Once in go to wireless settings and temporarily disable wireless security. when you get a reliable connection wirelessly between router and laptop you may apply wireless security, creating a passphrase, noting the HEX code this produces and applying it to the laptop's wireless adapter user interface.
If you have no joy, you might consider upgrading to a more recent router which will offer potentially better speed and security options.