Problem 173

Solution:
(I) Since $f(x)=\log_{2}(16^{x}+k)-2x=\log_{2}(4^{x}+ \frac{k}{4^{x}})$,
Therefore, $f(-x)=\log_{2}(4^{-x}+ \frac{k}{4^{-x}})=\log_{2}(k4^{x}+4^{-x})$,
From $f(-x)=f(x)$ always holding, we get $k=1$.
(II) Since $\log_{2}(4^{x}+4^{-x})$, let $t=4^{x}$, given $x\in[-1, \frac{1}{2}]$,
Therefore, $t\in[\frac{1}{4},2]$,
Since the function $y=t+ \frac{1}{t}$ is increasing on $[\frac{1}{4},1]$ and decreasing on $[1,2]$,
Therefore, when $t=1$, i.e., $x=0$, the function $f(x)$ has its minimum value $f(0)=1$,
Therefore, when $t= \frac{1}{4}$, i.e., $x=-1$, the function $f(x)$ has its maximum value $f(-1)=\log_{2} \frac{17}{4}$,
Since $m-1\leqslant f(x)\leqslant 2m+\log_{2}17$ holds for all $x\in[-1, \frac{1}{2}]$,
Therefore, $m-1\leqslant 1$ and $\log_{2} \frac{17}{4}\leqslant 2m+\log_{2}17$.
Solving gives $-1\leqslant m\leqslant 2$
Hence, the range of $m$ is $\boxed{[-1,2]}$.