Use mulitple SSID's for differant encryption
Nowadays almost every WiFi router supports multiple SSID's (I bought one for 13 pounds this month), and I use one SSID with WPA2-AES encryption for the 'N' devices and a second guest SSID for the Nintendo DS's with WEP encryption. Yes they do share the same channel but at least I can connect via the two types of encryption to give me 'N' throughput as well as legacy 'G' connectivity.