There were a couple of little problems. For example, Mathematica is case sensitive, i.e. Sin is different from sin. "Cross" is the vector cross product, and I suppose you mean the standard product. Also, when you post you might want to use code boxes. The following should work:
Sum[(Sin[Pi i/2]*Sin[Pi j/2]) (i^2 + (j^2 0.3))/(i^4 + 2 i^2 j^2 + j^4), {i, 1, 9}, {j, 1, 9}]
Cheers,
Marco
