It doesn't 'need' a memory card (Memory Stick is a Sony card, the DSi uses SD cards), you can play games without using one. A memory card would be for storing lots of photographs, MP3s or DSi store games.
no.
You need an SD memory card.
If you format your dsi everything will erase from your dsi including ur things from your memory card.
No, but it helps if you want to store a lot of media because the DSi only has a limited amount of space. But music can ONLY be stored it on a SD card and NOT the DSi's memory.
well unless you have a memory card it will be harder if you do then you load them on the memory card and just plug that in the dsi that should work otherwise you need a usb cable with the dsi tip and you have to plug it in to the computer with the usb and select the pictures that you want and load them to the internal memory if you don't have a memory card then i sagest getting one
No, the only things you can insert in a DSi is headphones/ ear plugs, a game and an SD Card.
Only when you have filled up the DSi's 256mb internal memory
No, you do not.
yes
Yes, the DSi (and XL) use the same memory cards as the Wii does.
Cartridge-based games will save to the cartridge. A memory card is necessary only if you download DSi-ware games from the shop.