1) vmlinuz 2) initrd.gz 3) syslinux.cfg 4) xxxxx.iso --> The iso which you want to install
Remember, do not use vmlinuz and initrd.gz in iso file here,
or the installng process can't read iso from your usb stick
vi syslinux.cfg
default vmlinuz
append initrd=initrd.gz ramdisk_size=12000 root=/dev/ram rw
syslinux /dev/sdx
ok, we finished all the procedure,now you can reboot your machine
Reference:
http://linux.simple.be/debian/usb
http://www.unicom.com/blog/entry/563
http://www.debian.org/releases/stable/amd64/ch04s03.html.en
http://www.vlug.org/pipermail/discuss/2009-June/026878.html