According to the instruction manual, Game Boy games do not work on the Nintendo DS. Game Boy Advance games can be played on the Nintendo DS and Nintendo DS Lite (but not any newer model) using the Slot 2 on the back of the console.
No only Gameboy games are compatible with the regular Gameboy.
No.
Yes, it can. This question has been asked multiple times and it is pretty clear that the game slot is exactly the same, if it wasn't then they would have made a total new game range for the DSi alone which wouldn't be necessary, they just added the two camera's, made it thinner and made Audio and Video files playable! And not forgetting the SD card slot.
yes, there is a slot at the bottom for GBA games.
With a 'regular' game, presumably everything you need to play it is provided in the original box. With collectible games, you can play the game using a starter set, but there are other things you can buy for it that can be used too.
if you have a hard drive you can play the xbox game's
They play 15 regular season games and three preseason games in the US plus one preseason game and one regular season in Canada.
No you can only play PS2 or PS1 games on your PS2. You can also play DVDs and CDs
You can't play 3DS games on the NDS in the first place.
Don't worry, it will. You just can't play them in 3d. If you want to play games in 3d, you'll have to buy a 3ds game.
Yes, regular DS games are not region locked.
ds regular and ds lite, not sure bout dsi though