Hello,
You can have IRE 1.1 and Cisco Unified client configurations simultaneously on a single PIX configuration. The EasyVPN configuration is vastly simplified compared to the legacy client.
The deployment of the 3.5x client is very nice as well. If using Pre-Shared keys then the setup on the client side is very simple. Also if client certificates are in use then the upgrade of the IRE 1.1 client is fairly straight forward as well.
Automated deployment is as simple as pre-creating a vpngroup .pcf file and distributing it to the clients with the new software, with the pcf file in the install directory.
Lookup the vpngroup command in 6.x documentation. This is all that is needed to add the ability for the 3.5x client to connect to a PIX with Cisco Secure VPN 1.1 client config enabled.
Here is a link to the command ref for 6.2 PIX code
http://www.cisco.com/univercd/cc/td/doc/product/iaabu/pix/pix_62/cmdref/tz.htm#xtocid12
Hope this is helpful
Jason Parrish
jparrish@rightsys.com