If i used same login for same pool with same worker on two different PC's would this make problems? would i be compensated for both or something would make it conflict
You can use up to 20 miners with same worker account at DeepBit if you want to take advantage of Long Polling. Using more than 20 will switch LP off and your stale shares percentage may increase.
Using different worker accounts is much more convenient as you may see which one is working and which one is not.
And remember that botnets are not allowed on many mining pools.