Even if you don't have a high end PC you can play it with all excitement. But a broadband connection is must.
If you have a good graphics card you can get the maximum out of this game.
But some levels are very hard and its like you will never finish it but if it becomes too boring the best thing is too play online.
If you convert your account by buying a paid version of the game which is TrackMania United you will have access to additional levels and environment and you can also use custom cars online.
Even in this free edition you can play with custom cars but the only disadvantage is that other players can't see it when you take it online.
But they only see the default car.
And your internet speed can be just 256kbps and it works fine.
But if you are not interested in any thing like additional levels and environments but you desire to just play online this free game is all you need.