converting expressions into latex code

You can produce latex code for the function you are taking a limit of and then just add the limit by hand:

sage: expr = (sin(tan(x))-tan(sin(x)))/x^7
sage: latex_limit = '$\\lim_{x \\to 0}' + latex(expr) + '$'
sage: view(latex_limit)

$\lim_{x \to 0}\frac{\sin\left(\tan\left(x\right)\right) - \tan\left(\sin\left(x\right)\right)}{x^{7}}$

By the way, some expressions in Sage take an optional parameter hold which prevents evaluation of symbolic expressions, e.g.

sage: sin(2*pi)
0
sage: sin(2*pi, hold=True)
sin(2*pi)

But the limit function doesn't take this parameter.