Most WPA routers support WEP too, just not at the same time. So you could Piggy back a WEP router on a WPA router ( DS -- WEP Router __ WPA Router __ internet ( -- is wireless, __ is wired)).
Also i think i read somewhere that theres a USB dongle you can use to get WIFI access in the DS. Attaches to a computer and the DS connects to that instead of the WPA network.
WEP = no real security. It gives the info needed to crack it to anyone who listens. Can be cracked in seconds.
WPA = wide range level of security. Default or Anything found in a dictionary as base passphrase = really lousy security.
That being said, if someone wants into your wireless network, WPA or not, they can get in. WPA is crackable, its stregenth is based your password. If your password is Eatatjoes, it'll be cracked easily. Best security = Random 64 character passphrase.
so a few things to consider. Do you really need that level of security? Do you mind spending the $$ on an extra router? Can you get a hold of the Dongle thing?
Basically if you don't need that security for wireless, then you can just switch to WEP and be done with it. If you do need the security, either piggy back or get the dongle.