Hi Friend,
The latest in 12.4 release is 12.4(13) and the feature set which you are running is
Enterprise/FW/IDS PLUS IPSEC 3DES
And the release i,age will be "c3660-jk9o3s-mz.12.4-13.bin " not sure if its a GD release in 12.4 train.
Also it required DRAM / Min Flash 128 / 64
To check for more releases you can use Feature navigator tool
http://tools.cisco.com/ITDIT/CFN/jsp/index.jsp
HTH
Ankur
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