How can I get it to play games of my external HDD?
Games under 4GB can be played from an ISO image with OpenPS2Loader. You just have to give them the right name and put them in the right folder or you can rip them with USBextreme or USBUlits. Games over 4GB will have to be ripped with USBextreme or USBUtils because of the 4GB file limit of the FAT32 file system.