Instead of running it on an OS that may already be infected, backdoored, keylogged or screenshotted by a virus or trojan horse you've already got, I would recommend running a liveCD and generating the key there. That way there is no chance of an eavesdropper intercepting the key, and it will not be written to the hard drive accidentally even as memory page file. See the last link in my signature.
This is good advice. I tried this the other day and and realized a couple things. First, generating the paper wallet offline from the bitaddress.org.html file worked fine. 2nd, when I tried to add encryption to the paper wallet, it would never complete because the browser could not execute javascript code. I tried a different live CD and ran into the same issue. In the end, I disconnected my iMac from the internet, ran the offline generator, and then encrypted the paper wallet. I then moved it to a USB drive (while still offline). Maybe some live CDs can execute javascript within the browser and I just had bad luck with the two I chose. I'm not sure. I know this isn't the most secure option of generating paper wallets, but it is what it is.
