So people know you don't need a GBA Flash card for this.
I tryed doing this at work but I didn't have the right wireless card, BUT when I got home that night and tryed it again with my PC I lucked out and had the right Wireless card.
How the whole thing works is rather simple really.
First and Most important you need a certen Wireless network card in your PC:
List can be found here:
http://damien.bergamini.free.fr/ral/list.html
Then you have to install these driver over your wireless card's real driver:
http://users.belgacom.net/bn967347/rt2560_driver_1_0_0_8.zip
This step by step is decent you only need to read the part on how to install the card, after that is not needed, Just read the rest that I wrote.
http://www.aaronrogers.com/nintendods/wifime.php
Then you Download 'Nintendo DS - Wireless Multiboot Application'
http://users.belgacom.net/bn967347/rt2560_app_wmb_1_4_beta_1.zip
Then you copy the Demos into the 'data' folder in the 'Nintendo DS - Wireless Multiboot Application' Folder. then you boot up 'Command Prompt' and type in:
(example)
C:\DS_Hack>wmb.exe -channel 1 -data "polarium_demo_usa.nds"
Then start up your DS, select 'DS Download Play' and it downloads it to your DS.
They key thou is the card, A VERY select few work. And the version is also important with some. At work I had a 'Linksys WUSB54G' BUT the problem is its a v2 not a v4 so it didn't work.