You can split a formula up among separate cells, and have each cell perform
its own calculation. Then, in another cell, reference those two (or three)
cells for your final calculation.
Also, you could download the Trial version of XL 2007, which greatly
increases the length of XL formulas.
Finally, you could describe what you're trying to do in a response to this
post, and perhaps someone can come up with a more efficient way of getting
done what you're trying to do. Frankly, I have never seen a legitimate need
for an exceptionally long formula, in which there was no way to accomplish
the same thing in a more compact syntax. Of course, I can be proven wrong
here.
Dave