The new juniper 6.5 client seems work with OSX 10.6.x better than the old ones did – it no longer requires creating a directory and setting permissions from the command line.
That said, my upgrade seemed to go ok, but a few days later, it stopped working – saying it was unable to download files from the URL of my webvpn.
I did an uninstall (I used appdelete) then downloaded the VPN client from the VPN
it turns out the client is easily obtained manually by using
(URL of your webvpn)/dana-cached/nc/NetworkConnect.dmg
this downloads the disk image file, then you can run the setup program from there – once I did that, it worked fine without any further modifications.
(thanks to William (post #9) on http://forums.juniper.net/t5/SSL-VPN/Snow-Leopard-Network-Connect-Fix/m-p/29985)