No. I tried that once on a Wii with no success-

Get a usb- wireless softap or a router.

 

Assuming you don´t have a compatible wireless card, you might want to look for a router.

Personally, i use connectify in my laptop along my 2 wireless mini pci cards.
One´s IntelProWireless which it´s not supported by connectify, and the main one. The second it IS supported by connectify, being a AR5600X atheros.

However connectify (or windows 7) won´t let you set up a SOFTAP security level lower than WPA-2.

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But yes, as far as i know, there´s NO way to connect a Nintendo devide to had hoc, even if it´s supported by hardware design. Just wifi infraestructure mode.

 

Windows 7 + Compatible wifi chipset should do the trick

You can check that by looking at networking properties. If you see something like "Microsoft Virtual Network adapter" which dissapears when you disable your current atheros wireless chipset, then you have the possibility to get SOFTAP in Windows 7. That´s due to one of Windows 7´s hidden possibilities to mount a SoftAP. Connectify acts as a "gui" interface to "enable" the same thing i´ve mentioned before.

On topic, even if you manage to mount a SoftAP through Windows 7, sadly it won´t work with Nintendo DS due to higher encryption security language. DS supports up to WEP (Both DS phat/DSLite), while in WIFI mode. Windows 7´s SoftAP mode, offers you WPA-2 ONLY. (Which means there´s no possibility to downgrade security level to WPA, WEP)

However I´ve tried ATHEROS AR5600X (my chipset) along Connectify and Windows 7, to connect my wii, and worked like a charm, even with homebrew apps.

; ) Hope that clarify some questions.