The Nintendo DS Lite cannot natively play Game Boy Advance cartridges. The GBA slot was removed (DS Phat only). However, you can play GBA games via flashcarts or emulation.
DS Lite lacks Slot-2. Only original DS "Phat" supports Slot-2 carts (EZ-Flash IV, M3 Perfect, Supercard MiniSD).
Downloading ROMs for games you don't own is copyright infringement. Dump your own carts (using GBxCart RW, OpenLara, or DS flashcart + GodMode9 on 3DS) for legal backups.