For forwarders its generally best to use hiyaCFW as that allows you to keep the menu music and splash screen, without which its almost further from stock then just using TWiLight. Personally I just use TWiLight Menu++ and have it autoboot directly from Unlaunch, but forwarders can be a good option if you really want to use the official DSi Menu. He claims it works (but has been too busy with work. Supposedly it involves putting the Acekard2i files on the SD and then putting the roms in the Games folder.

If you don't want to have to use hiyaCFW you can also use NTM to install the forwarders to the SysNAND menu, but this comes with a couple caveats: A) you'll still need Unlaunch and its launcher patches will need to be enabled since they're not legit DSiWare, which disables sound in the DSi Menu and the health and safety splash and B) no matter what you'll still need the SD card in to actually play the games as only the forwarders are on NAND, the games themselves are still on the SD. My roommates friend bought a DSi the night it came out, and he explained over the phone that there was a way to play NDS roms on the SD card without getting a flash. I chose the NDS Lite over the PSP as my initial purchase simply because I wanted to explore the features available through the touch-screen. That guide assumes you have hiyaCFW which in turn relies on Unlaunch from the main guide CoolMe linked. Step 1: The Need to Hack the Nintendo DS Lite I recently took the plunge and tried out mobile gaming and my life will never be the same. For cart games on the DSi Menu it's also possible to use forwarders instead of/in addition to TWiLight Menu++.

Dsi hacking without flash card