SSH works regardless of how your computers are connected. It's just an IP (TCP) based protocol. Whether you have a router, a WLAN, or a 3G connection is irrelevant.

Now. Make sure both your computer and your N900 have an IP address and a proper routing table (= are connected to the internet, try loading the google.com webpage or whatever).

If both are connected, then ssh from your computer to your N900. If it doesn't work, report on another thread (or possibly in another forum, as the problem might be related to your connection, cable modem, etc, etc.)

Good luck. But please stop "spamming" (whether you agree with the term or not), because your problem is NOT related to KP48.