+1, is the clutch fluid up to the mark on the window in the reservoir? And, if it is, is it clean?
If the fluid gets dirty enough, it won't shift well. If it gets low it will do what you're describing (this usually means a clutch slave cylinder rebuild, very easy and not much $$$).
Finally, if the engine oil is truly foul, I have a hard time shifting....but I think not as hard a time as you're having....