If you want to stored the games on the standard xbox hard disk: Do a search for ISO2GOD, this converts the ISOs to games on demand (GOD) format. These then need to be transfered to the xbox hard disk. You can use the XEXMenu to copy these from a USB to the xbox hard disk or look at JTAG Content manager (i think is the name) which will FTP the data straight from the PC to the XEXMenu FTP server.
If you want to store on an external USB hard disk: Extract the contents of the ISO to a folder call GAMES on the USB hard disk. The USB hard disk must be FAT32 formatted. Then boot into freestyle dash and star a scan.
I keep mine on the xbox hard disk so not entirely sure what apps are needed for the USB storage.
Still quite a noob myself