When I want to go online (WiFi multiplayer for the first time) there's a message that says that the game-module will be linked to my DS and a friends code will be created.

No problem with the second part of the message but does the first part mean, that I can't use my game-module in other DS-Systems anymore after linking the module together with my DS? I'm a little bit scared to just try it out... :eek:

Greetings
Loco

Your online profile is tied to your card and DS console. You create your online profile for one specific console, you cannot use it on another console. Trying to do so will result in the game asking you to create a new profile (overwriting the old one).
edit: this is only for your online profile, you can use single player and local multiplayer using the same card on a different DS console.

OK - thank you so far.
One more question: Does the DS support WPA or only WEP?

Greetings
Loco

http://www.nintendowifi.co.uk/consumerservice/wfcGlossary.do
WPA Security
A method of encryption (as opposed to WEP) used by routers to protect against unauthorized network access. The Nintendo DS is not compatible with the WPA method or any other methods of security other than WEP.