I am pretty sure one is the Red Gyarados and Dialga (On the cover of your DS game case) I've got the Red Gyarados and got it from the Lake Of Rage but I think that's in Heart Gold. But I have a Luxray which evolves from a Luxio which that evoles from a Shinx. Hope you find the rest of them!
you can't catch it because you already beaten the legendary
no
you can start over
5
Yes quite a lot of them
there is no best spot
catch legendary Pokemon like giratina and heatran
uxie azelf dialga, mespirite, girantina and heetran
You'll have to have received it from a special event.
you have to catch Palkia(in pearl)orDialga(in diamond)
Not much. Pokemon diamond and Pokemon pearl have different Pokemon. for example, in pearl you can catch a glameow but not a cranidos and in diamond you can catch a cranidos but not a gleameow. And at the end of pearl you can catch Palkia the legendary and at the end of Diamond you can catch Diagla. But the games are basically the same. And there you go.....
No, in Diamond and Pearl you can't catch the legendary birds.