Russia invaded Poland with Germany in 1939.
You forgot about Poland invasion of Russian Belarus and Ukraine in 1919 contrary to the Curzon line, which was the official border of the Soviet Russia at that time.
They were allies then.
No, they weren't allies. Or they were the same allies as Poles were - because Poland also had a treaty with Germany - German-Polish non-aggression pact:
http://en.wikipedia.org/wiki/German%E2%80%93Polish_Non-Aggression_Pact
I was only replaying to people who still don't know that Katyn Masacre was done by Stalins order.
The contrary opinion (that massacre was done by nazis) was proven by international commission. The fact that some politicians, like Gorbachev and Medvedev, prefer to betray their nation and oppose the truth, doesn't change anything.