So, is this your case?
What Operating System are you running at your computer 1? If you have an already working Debian system on HDD1, you could just clone it to HDD2 and run without any installation. Just use bitwise copy program
dd if=/dev/sda of=/dev/sdb
I assume here that HDD1 is
/dev/sda and HDD2 is
/dev/sdb Then before plugging HDD2 of the computer 1, try to change device boot order in BIOS and try to boot from HDD2, not HDD1 as usual.
WARNING0: I suppose, that your HDD2 doesn't contain any information and you can overwrite it totally.
WARNING1: make sure, that your /dev/sdb corresponds to HDD2; if it corresponds to HDD1, you could overwrite your OS on computer 1.
Debian suggests another way: http://www.debian.org/releases/stable/amd64/apas02.html.en#howto-getting-images-hard-disk, see booting from hard disk. They suggest, that you partition you HDD2, put kernel image and initrd ramdisk onto a boot partition and copy and .iso file somewhere on that disk. Then, you install bootloader there, e.g. GRUB, reboot from that disk, GRUB loads kernel and ramdisk, kernel somehow finds the .iso image with installer and starts it.
Ok, I decided to write a digestion of how I would've done the whole thing, but I'm not sure about certain points. It's just what I'd do at your place.
I assume, that you don't have any valuable information on you hdd2. I also assume, that you run Windows on Computer1 off HDD1.
1) Partition your HDD2 with some partitioning tool. You'll have 1 partition, where the installer will reside and it will stay untouched during the installation process. I'd put the installer partition to the back side of the HDD2, cause, I'd have it removed after I install Debian.
There can be no more than 4 primary partitions on a disk with MBR. If you want more, you can create a special Extended partition and create logical partitions within it. Linux is ok with logical partitions, Windows used to have troubles.
2) Download hd-media installation kernel image (vmlinuz), installation ramdisk () and installer image () e.g. from debian archive: http://ftp.debian.org/debian/dists/squeeze/main/installer-i386/current/images/hd-media/ and put them to the Installer partition of HDD2. Note that this link is for
i386 architecture, if you want e.g. 686 (64-bit) kernel, load it from appropriate (686) folder of debian ftp.
3) Install GRUB to the MBR, DOS compatibility region and/or beginning of your installer partition. See this to understand, where GRUB resides and how it works. As you're using Windows, you'll have to use something like GRUB4DOS.
GRUB configuration should be as described here. Or you can use other bootloaders, such as LILO or Loadlin, they should be better suited for running kernel from NTFS or FAT filesystems, used by Windows machines. Consult to Debian website.
4) Plug HDD2 off and attach it to computer2; set device boot priority in BIOS to boot from HDD2.
6) Try to boot the HDD2. Hopefully, BIOS will start GRUB, GRUB will start the installation kernel, supply it with installation ramdisk, kernel will start, mount the installation ramdisk, installation ramdisk will start its
init script will mount the installer image and run
init script of the installer. Installer will start and show you interface, where you could change partitions on HDD2, choose partitioning scheme and finally install Debian.
7*) Boot Debian. Optionally you can remove installer partition (e.g. with
GParted) and merge the free space with