games not playing :(

hey, ive downloaded a few games from this website and others which are specifically made for the nokia n900 but when i go to open the game it asks for the app it should use to open the file... what file do i use to open and use the app/game?? i havnt dowloaded any kind of software and only have the software the phone comes with...

please help because i love my phone and really want to play all the games i can! im sure you all understand!
also if i download from the ovi store of app manager it plays and loads fine... just not from any other website which is no good because the games from ovi are a bit boring.... Smiley

thanks for your help.

Sammy