smc

We can use difference of squares to factor the denominator, yielding: $\frac{1000^2}{252^2-248^2}=\frac{1000^2}{(252-248)(252+248)}=\frac{1000^2}{(4)(500)}=\frac{1000^2}{2000}$. We see that the $1000$ in the denominator cancels with one of the $1000$s in the numerator, yielding $500,\boxed{500}$.