On this page there's a howto about how to wifime with your Nintendo USB stick (or any other rt2570/rt2500usb device) via Windows or Linux.
It uses either a knoppix boot cd (leaving your system intact, no changes done) or VMplayer.
The guide requires you to have:
Winzip/Winrar, or any other application capable of opening/extracting a .zip file.
A vmdk file downloadable from the site.
An usb stick supported by the driver, with the rt2570 chipset (like the official Nintendo WiFi dongle).
The Knoppix live iso CD (only tested with version 4.0.2 -> working)
VMplayer (only tested with original release version),
Any official Nintendo demo (or other .nds with an official RSA).
A working computer .
Optional An usb data stick
This clears out the general myth (that even survives in the DSlinux wiki) that WMB/Wifime can not be done with USB sticks or without Windows.
There are also pictures of the insides of a GBAMP and SC-CF there, and a beginnersguide to DS
homebrew (unfinished).
Feedback via comments
______________note____________
*All content in the vdmk file (exept for the shells) is released under the GNU/GPL license, the original files can be found here.
Thanks Masscat!
*edit/update* a flashme guide was just added, thanks tc1415 .