Copied almost verbatim from Leo Li (thanks):
1. Download the required files from the below address:
http://www.mediafire.com/download.php?ssadit26tl3llms
2. Configure GNS3 preferrences -> QEMU -> ASA with below settings
RAM: 1024 MiB
Number of NICs: 6
Qemu options: -m 1024 -icount auto -hdachs 980,16,32
Initrd: C:\ASA\asa842-initrd.gz
Kernel: C:\ASA\asa842-vmlinuz
Kernel cmd line: -append ide_generic.probe_mask=0x01 ide_core.chs=0.0:980,16,32 auto nousb console=ttyS0,9600 bigphysarea=65536
3. Activate the license using the below code:
activation-key 0x4a3ec071 0x0d86fbf6 0x7cb1bc48 0x8b48b8b0 0xf317c0b5
