I’ve had issues getting Juniper’s Network Connect app to work on Snow Leopard. First up, it simply wouldn’t install at all, which was a bit of a problem.
Turns out you can download the dmg from the firewall through the url /dana-cached/nc/NetworkConnect.dmg – eg, if you’re connecting to example.com then the url will be https://example.com/dana-cached/nc/NetworkConnect.dmg (No, I’m not making that URL a hyperlink!)
Then, once it’s downloaded and installed you need to update the permissions on one directory and create another:
sudo chmod 755 /usr/local/juniper/nc/[version number]/
sudo mkdir ‘/Applications/Network Connect.app/Contents/Frameworks’
This worked for me using version 6.4.0 on Mac OS X 10.6.2