It depends which Windows version you mean.
See below from the VPN FAQ: http://www.cisco.com/en/US/products/sw/secursw/ps2308/products_qanda_item09186a00801c2dbe.shtml
"Cisco VPN Client ver 5.0.07 supports Windows Vista and Windows 7 in both the x86 (32-bit) and x64 (64-bit) editions.
Cisco VPN Client does support Windows XP 32 bit only, but Windows XP 64 bit is not supported."
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