I want to connect my DS so I need to turn off
router security temporarily, or change it to
WEP, but if thats gonna have any long term
implications (Changing security data on my
laptops, computer and PS3) then I'd rather just
turn it off for a few minutes. If anyone can
explain in the simplest way possible I'd
appreciate it (Step by step, I'm kinda slow)
Thanks =]

If you want your DS to access the net then the only option is to reset your router security encryption to WEP on shared key sequence #1 Your router manual will contain details on how to configure it.
You will then have to re-configure each wireless client system with the new security key. This will not affect any wired client systems.
As for long term possible consequences, WEP as a security protocol is practically useless against any savvy hacker. It can be broken in about 15 minutes. Mine was accessed in the middle of the night by a passerby who parked outside my home.
Goin' Fishin' (Some day)
If I do that can I change it back afterwards then? I don't want non
secure internet...
It sounds like you have to set the router to use WEP as long as the DS is accessing it. You can change it back, but you'll have to change it back-back (to WEP) anytime you want to use the DS online.
