I have upgraded to RC5 0.5 XP SP 3. I have encrypted the wallet. How do I know if it worked for sure?
To be absolutely sure, you need to extract your private keys and then run a tool to look for them in your wallet.dat file (or other files on your disk).
If you are able to compile a custom version of bitcoin and run python, here's how:
https://gist.github.com/1361001
If you can't compile a custom version of bitcoin or run python code, then you'll have to trust other people to thoroughly test.