I’ve come across multiple ways of doing it but so far the best way is the following (I assume you are on i386 platform and you have access to the net):
1. Download boot.img.gz from Debian website
2. Download the net-install image choosing i386.
3. Plug your USB drive into a Linux PC, open the shell and type

$ dmesg

Last few lines should be like the following:

 sd 7:0:0:0: [sdb] Attached SCSI removable disk
 sd 8:0:0:0: [sdb] 4030464 512-byte logical blocks: (2.06 GB/1.92 GiB)
 sd 8:0:0:0: [sdb] Write Protect is off

Now we know it has been mapped as sdb

4. Use zcat to load the boot.img.gz onto your USB drive

# zcat boot.img.gz > /dev/sdb

CAUTION!!! this will destroy the entire data on the USB drive, make sure you have done the backup.
If you get an error ensure the following:
- You are root (don’t use sudo)
- The USB drive it’s not mounted, if it is umount it before issuing the above command.

5. Now mount the USB drive and copy the net-inst.iso image on it.

All done! Now plug it into the box you want to setup and enjoy the old fashion Debian installer