Environment variable for Windows Questions

I'm having a hard time trying to get multiple environment variables configured at the same time. Here are some issues that I would like answered:

1. If I do have spaces in my PATH environment variable (i.e. C:\Program Files\Java\jdk1.6.0_25), is there any way to keep the same path, but make sure that nothing unexpected happe开发者_运维知识库ns? I keep hearing that you shouldn't use spaces like in this link here: http://ist.berkeley.edu/as-ag/technology/howto/install-java-sdk-win.html.
2. Is there a difference in the ordering of the environment variables as listed in the fields?
3. What will happen if environment variables in the "User variables for user" fields and the "System variable" fields are different? Is it safe to assume that the result will be all the fields combined for that particular variable?

Thanks for any advice!