[Tutorial] DeSmuME Wi-Fi With a Wireless Connection (Read Description)
80UPDATE: On the 20th of May 2014, Nintendo shut down the Wi-Fi network for the DS and Wii, meaning that aside from the DS store, no Wi-Fi connections are available on the DS anymore. 3DS games are unaffected, but you can't work around the issue by playing DS games on a 2/3DS :( Thankfully, there is still a way so a new video shall be up soon!
Someone has started a petition on change.org to stop Nintendo from shutting down Wi-Fi for the DS and Wii. You can find it here: https://www.change.org/petitions/nintendo-keep-the-nintendo-wii-wi-fi-connections-on
This is a very advanced topic. Unless you understand how the internet works and how VMWare can be used to emulate wired equivalent privacy (WEP), this is probably too complicated!
Notice: I have had issues with Pokémon Battling with myself using this. I know that most people who use DeSmuME with Wi-Fi will probably be using it for Pokémon-related things (knowing how popular it is). This simply shows how to make a connection to the internet, not have a Wi-Fi battle. I have tried this by downloading things from the internet in games, and it worked.
LINKS IN DESCRIPTION
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DeSmuME Wi-Fi version:
http://www.mediafire.com/download/phwq7fgnpnxi92d/Game_Source_Code.rar
Note: Links for Windows 7 ISOs are down since 30/01/2014. Digital River stopped distributing them. :(
So I finally figured out that it was possible to get Wi-Fi on DeSmuME, using a Virtual Machine.
If the Virtual Machine itself is slow, you can disable visual effects (I disabled Aero and went back to the classic Win95 theme). If your computer is slow, exclude the Virtual Machine folder from your antivirus. It won't be able to detect things on your Virtual Hard Drive, and if it is being used, it might be constantly getting scanned by your antivirus.
Please note: You DO have to run the emulator in the VM if you don't have a Wired connection. With a bit of lag, most computers should work fine; if they don't, disable visual effects (look this up on the internet) in the virtual machine.
x86 Windows 7 will require 1 GB RAM or higher allocated to it in order to run, and x64 Windows 7 will require 2 GB RAM or higher allocated to it in order to run. I suggest creating a 20 GB virtual hard drive.
Upon exiting the virtual machine, for about 5-10 minutes, your computer will lag tremendously. To fix this, open the virtual machine .vmx file in notepad and put these three lines of code in at the end:
mainMem.useNamedFile = "FALSE"
prefvmx.useRecommendedLockedMemSize = "TRUE"
prefvmx.minVmMemPct = "100"
VMWare tutorials can be found all over the internet. When you download the .iso files, you don't need to burn them to a disk, you can put it in the VM's virtual disk drive.
If 64-bit mode isn't working and you have a 64 bit computer, then it is most likely due to Intel VT-x / AMD-V. Toggle it enabled/disabled in your BIOS.
IMPORTANT: If you are using a 64 bit virtual OS (and any good computer nowadays is 64-bit), you MUST run the x64 DeSmuME. Always run as administrator.