Don't forget that the Poles cracked the code for the Enigma machine.
"The German military model, the Wehrmacht Enigma, is the version most commonly discussed. The machine has gained notoriety because Allied cryptologists were able to decrypt a large number of messages that had been enciphered on the machine. Decryption was made in 1932 by Polish cryptographers Marian Rejewski, Jerzy Różycki and Henryk Zygalski from Cipher Bureau. In mid-1939 reconstruction and decryption methods were delivered from Poland to Britain and France. The intelligence gained through this source—codenamed ULTRA—was a significant aid to the Allied war effort. T
he exact influence of ULTRA is debated, but a typical assessment is that the end of the European war was hastened by two years because of the decryption of German ciphers."
http://en.wikipedia.org/wiki/Enigma_machine
It can also be added that the Polish military consisted of 1.7m soldiers (a lot for a 30m populated country), but only 900k were employed largely due to confusion in the first days of the invasion. German planes also bombed most of the main transportation/communication centers making it even harder for the Poles to organize a decent defense, and out of those 900k only ~200k had reached their assigned units on August 31.
The Polish army was "large" in essence, but it was horribly equipped. The infantry, the tanks, planes everything was out-dated. There was also a great lack of anti-tank guns. There were already newer models of tanks&planes in production or at least on the drawing table in 1939, but the Poles weren't expecting a war until 1942 (that is when their 10 year non-aggression pact with Germany ended), therefore all their war preparation was based on that.
I believe Poland couldn't had done much more in preparation for the war,being a financially weak nation and already pouring 1/3 of its income into the military. After all it had just regained its independence 20 years before the war and at that time the country was a mess and in the first years the Governments expanses were 3x larger than the income.
Poland's big mistake was trying to keep an equilibrium between Germany & Russia and counting too much on their British and France allies. Poland didn't want to side with Germany to not provoke Russia and via versa.
The sad fact remains that France had a larger and more powerful army than Germany at the start of the war, if they would had the courage to invade Germany then perhaps Europe could had been saved from the war.