What is a RELIABLE way to detect a client’s browser and its version number?

What is a reliable way to detect someone’s browser and its version number? From what I’ve seen, things like the navigator object in JavaScript simply do not work toward this end, and neither do a lot of these really hacked-together solutions I’m coming across. There are one or two currently functional JavaScript code snippets I’ve come across that’ll tell me whether someone is using Firefox, Chrome, etc., but they don’t describe the version number of each browser. How can this be found, and how can it be done reliably? (The front-ends are a couple of Flex applications.)

How to make a Python script run like a service or daemon in Linux

I have written a Python script that checks a certain e-mail address and passes new e-mails to an external program. How can I get this script to execute 24/7, such as turning it into daemon or service in Linux. Would I also need a loop that never ends in the program, or can it be done by just having the code re executed multiple times?

Driving Excel from Python in Windows

We have various spreadsheets that employ deliciously complicated macros and third party extensions to produce complicated models. I’m working on a project that involves slightly tweaking various inputs and seeing the results. Rather than doing this by hand or writing VBA, I’d like to see if I can write a python script to drive this. In other words, the python script will start up, load the excel sheet, and then interact with the sheet by making minor changes in some cells and seeing how they affect other cells.