You can already extract the secpack with existing tools.
Download the firmware and unzip it - you're interested in 022-3896-4.dmg (or 022-3900-4.dmg)
Download 8900decryptor (C source, Win executable ...) from iPhone Elite web site (link not authorized) - compile it if necessary
Run 8900decryptor 022-3896-4.dmg ramdisk.dmg. ramdisk.dmg is the decrypted ramdisk image
Mount this image if you're on a Mac/Linux, or open it with MagicISO on Windows
Extract the FLS file from /usr/local/standalone/firmware in the ramdisk
Then extract the secpack according to http://iphonejtag.blogspot.com/2007/08/step-7.html
(ok, already posted, thanks Dborca :p)