...now, honestly, I have really no idea what the difference either of the encryptions are except that WPA allowed me to use a phrase/word as a password rather than using the bajillion numbers that the WEP passwords are. I really don't feel like doing that. Plus, I don't want to have to change the router settings and then tell my roommates why I did it just so I can play Mario Kart DS online. After doing a search (Processor.com has a great and easy to understand article on this), and a thread on the Penny Arcade Forums, i've found that the WPA is the best...for now...
...so, if you are having the problem like I am (and just didn't think about doing this), just get the Nintendo WiFi USB dongle, or the generic non Nintendo one which is what i'm doing thanks to Ebay. :) The WiFi USB dongle will create a WiFi access point from your computer that is already connected to the internet, may it be a wired or a wireless connection. When you're done, just unplug the dongle and the access point is gone! Simple as that...when I found out about this i just slapped my forehead and just thought...man...i'm stupid...