Composing Mathematics Papers

I was just wondering if anyone had recommendations for programs/document editors that are good for putting together professional-looking formulas and papers? Free and Windows-compatible is always nice, but "free" non-windows apps would work as well. A quick googling led to nothing of use.

Thanks guys.

Speaking of LaTeX, I'm a noob at it in need of tech support.

I have MiKTeX, and WinEdt (and TeXnicCenter), and I want to install (if that's the right word) a .cls file that I need to compile a certain .tex document. How do I install said .cls file?