Just wanted to throw this in there too: These headphones have 60Ohm impedance, which means some onboard sound chips in PCs / laptops might not handle it well. I know my sound chip didn't, cutting off the lows at higher volumes, so be sure yours is able to handle it, or maybe get a really cheap PCI ...

I just purchased the Audio-Technica ATH-M40fs headphones. I've set me mind to start producing electronic-dance music and eventually in the next month or two I will get a midi keyboard.
Should I get an interface or just get an 1/4" to 1/8" adapter from the local Radioshack?
If an audio interface is ...