[Shamun]

Your stuck using a standard text editor for templates. X-cart templates are pretty much only HTML/CSS/Javascript. The exception is smarty, but those are fairly easy to understand if you know English and good at inferring what the variables are for.

I personally use notepad++ for doing it. Seems to be the only editor that fully highlights opening/ending of code when clicked anywhere. Most others require you to click at the very start of it, and it doesnt really 'highlight'.
Couple that with firebug and you're golden.