Nintendo DS and Wii

I'm thinking about getting a DS, I commute for about 45 min twice a day so I think this makes sense.

Could you guys give me a hand with the following;

1. I have a Wii, do they interact with each other in any way Wi-Fi or w/e??

2. How much play time can you get out of that brain stuff?

3. Has anyone played the new pokemon as I found these were my favourite games back when I had a regular game boy.

4. Mario Kart is it any good. None of my friends have a DS so multi players out I think. Is it worth it if there is no multi player.

5. I know these things have memory cards on them but can they play media? if so what?

6. Considering I have a Wii will the DS kinda have to be better than the PSP? personal opinion on which one is better?

Thanks guys,

I really don't know a lot about these things but my video ipod is pretty scratched up. And i'm looking for something to replace it when I'm commuting.

Thanks again,