brew install python, but then: "python-2.7.6 already installed, it's just not linked"
It looks like you have installed Python using another method before. Don't be scared. Homebrew is engineered so it won't mess up your system like Mac Ports et al.
You can always do brew link --overwrite --dry-run python to see first what exactly will be overwritten, without actually doing it.
If once you do this it look like it is only overwriting or deleting *.py scripts, then you should be even less scared.