Hi,
Using Cisco VPN Client is highly recommended to be used with any Cisco VPN servers/devices such as VPN 3000 Concentrator, ASA5500 series and PIX Firewalls, including IOS devices e.g router that support VPN.
Beside compatibility issue, using this client allows you to fully utilised or maximize all features that can benefits your VPN access/network environemnt.
*http://www.cisco.com/en/US/partner/products/sw/secursw/ps2308/products_data_sheet0900aecd801a9de9.html
*http://www.cisco.com/en/US/partner/products/sw/secursw/ps2308/prod_release_note09186a00802d398a.html
As for the NetGear, they probably had a proprietry config/setup that meant for their client software. Personally, I've never test it with Cisco VPN Client.
Rgds,
AK