I wished to have that feature since a very long time ago and at last I found a solution which was very simple! The solution idea is simple: Don’t use your base OS to connect to the VPN, use a virtual machine instead, for example I use Virtualbox as my virtualization software and I have Ubuntu 9.04 as my base OS and Ubuntu 9.10 as my guest OS, I installed the Cisco-compatible vpnc and network-manager-vpnc packages, and then connected to the VPN on the guest OS and everything worked like a charm! On my base OS I can do everything I want as if I’m not connected to any VPN and my guest OS connects to the VPN and has access to all network resources there, simple, isn’t it 🙂 ?
Update: I did the same with a Windows XP guest and Cisco VPN client and it worked fine as expected.
Just Some Techie Notes! 
Good, But I think the Virtual box will give a performance less than the base one.
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This mainly will affect ppl that uses the VPN all the day long (like me )
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Yes, the performance is less, but that's only when you need to use something that needs high performance which is not in my case, I use the Windows VM for Internet explorer and Siebel Tools and the Ubuntu VM for running terminal commands and some other small stuff. The main advantage is that I open the Windows and Ubuntu guests and keep them connected to the VPN to do whatever I need form them while at the same time I'm connected to the Internet without any interruption.
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and by the way, I assigned 512 MB of RAM to each of them leaving me 1 GB for my host OS which is enough to keep me working fine on Linux.
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I use the same way to connect to a customer for 1.5 years now 🙂
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You should have written it in your blog then 🙂
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I agree 😀
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