Below provides the nessecary steps required to create an a packet capture on an ASA/PIX, and the relevant download method.

Note : You will requre pscp (putty pscp) installed onto your PC. Download pscp here.
Note : This is only available in the later versions of PIXos & ASAos.

1. Start Capture on PIX

capture capturefile type raw-data interface [interface name]

2. Enable scp and copy capture into Flash

ssh scopy enable
copy /pcap capture:capturefile flash:capturefile.cap

3. On your PC run the following syntax via 'Start | Run | CMD' to download the capture to your PC.

pscp -scp [user]@][PIX IP]:capturefile.cap capturefile.cap