edit Using Unetbootin

It is possible to install NixOS from a USB stick, rather than from a CD. This is useful if you want to install NixOS on a machine that doesn't have a CD-ROM drive (such as most netbooks), or if you don't want to waste a blank CD. Here is how to do it:

  1. Download a NixOS ISO image or create a custom ISO.
  2. Obtain a USB stick formatted with the VFAT/FAT32 filesystem with enough free disk space to hold the contents of the ISO image. Note that it's not necessary to erase the USB stick.
  3. Install UNetbootin, a tool that allows you to create a bootable USB stick from an ISO image. UNetbootin runs on both Linux and Windows. If you already have Nix/NixOS, you can install it by running nix-env -i unetbootin. Other tools may also work.
  4. Insert the USB stick, start UNetbootin, select the ISO file and target USB drive, and press Ok. This copies the contents of the ISO to the USB stick and installs the GRUB boot loader.
  5. You should now be able to boot NixOS from the USB stick, and perform the installation as usual.

edit Using syslinux

If you have trouble booting from a USB drive or sdcard with Unetbootin (I just got a blinking cursor instead of a bootloader on an Asus eee 1000) the procedure described on http://www.knoppix.net/wiki/Bootable_USB_Key should work. After preparing the sdcard with mkdiskimage and syslinux you can mount it and copy all the content from the NixOS iso: 

$ mount -o loop ~/Downloads/nixos-graphical-0.1pre27337-i686-linux.iso /media/iso
$ rsync -av --progress /media/iso/ /media/sd-card/

The syslinux.cfg needs to be created manually, but the details can easily be derived from the grub.cfg on the NixOS install cd.

I specified the root device by UUID, to get the UUID: 

blkid /dev/mmcblk0p1

The relevant section from the live cd: /media/sd-card/boot/grub/grub.cfg 

menuentry "NixOS Installer / Rescue" {
  linux /boot/bzImage init=/nix/store/r7xhnzymi1ll49r4glf1dwr5y1alx0bl-system/init root=LABEL=NIXOS_INSTALL_CD_0.1pre27337 splash=verbose vga=0x317
  initrd /boot/initrd
}

can be used in the syslinux config file: /media/sd-card/syslinux.cfg (you should just need to update the init path and the root UUID / LABEL or device path) 

DEFAULT linux
LABEL linux
  SAY Now booting the kernel from SYSLINUX...
  KERNEL /boot/bzImage
  APPEND init=/nix/store/r7xhnzymi1ll49r4glf1dwr5y1alx0bl-system/init root=UUID=509C-63E2 ro initrd=/boot/initrd splash=verbose
Retrieved from "http://nixos.org/wiki/Installing_NixOS_from_a_USB_stick"