What you need to get your hands on is a Grom kit, they sell for around £60+ you can get them for iphone/ipods, usb flash drive or bluetooth.
It is as easy as the vid shows to install one of these, around 10 mins and you'll have mp3 music playing through your standard stereo.
As for folders i think your limited to around 99, but have a look here, http://www.gromaudio.co.uk/tag/Lexus