If I bought someone's used 3ds xl that already has several games downloaded to it, is it possible for me to create my own username on that ds and still have access to those games?

Thanks in advance!

Yes. Game downloads are attached to the system, not to usernames. Enjoy those free games. :)

@kerned: Awesome! Thanks so much!

One more question... will I be able to move them to a new SD card?

I believe so, but they're tied to the 3DS they were bought on as far as I know.

@benny: Yes, looks like that's right. Thanks.

http://www.nintendo.com/consumer/systems/3ds/en_na/ht_settings.jsp?menu=data%20management&submenu=ctr-ht-settings-transfer-data-between-sd

So the replacement 3ds Nintendo should be sending me after mine broke 3 weeks in won't let any of the games I downloaded work?

Yippee...