If you don't have a wireless router here is my tutorial I thought of while trying to get free WiFi without a wireless router.
OK. Ready? I'm not POSITIVE I need someone to test it.
OK, now ready?
1.Get your DS charger
Cut it in half but keep the end that goes into the DS.
2.Get an extra USB cable. In the MIDDLE of it cut the thing in half. (MAKE SURE YOU HAVE THE FAT END READY TO USE)
3. I'm not sure what it's called, but put the USB's wire with the fat end and connect it to the DS's power cord you cut in half.
4. Plug it into your PC and you should have WiFi.
Tips:
[Make sure you put tape over the two wires you assemble].
[Like I said, I'm not sure if this works, if it does someone please post].