As for softmods, the only kind of softmods I ould know would be save game hacks. There aren't any mods for 360 like their are for the wii. The easiest firmware mod there is, would be flashing the DVD drive to read backup games, which could be considered softmod I guess, but its much more complicated than using an SD card to load up a custom firmware installer. You must open your console at the least.
If you are wanting homebrew, installing arcade games, etc, there are no softmods for (as far as I know). You must hardmod the console by soldering something new inside, allowing you to then connect to a pc to alter the 360 firmware. This way, from what I've read, is complicated if you don't know how to use a soldering iron, and is very dangerous online. You will most likely get your console banned from online play immediately.