The Cisco IPSec VPN Client supports Windows XP and Windows Vista 32-bit only. You need to ensure that Windows6.0-KB952876-x86.msu is installed with the 5.0.4 client.
Version 5.0.4 is what we recommend customers use.
More information on:
http://www.cisco.com/en/US/products/sw/secursw/ps2308/
Cisco VPN Client FAQ:
http://www.cisco.com/en/US/products/sw/secursw/ps2308/products_qanda_item09186a00801c2dbe.shtml