Pspice OpAmp Integrator Problem
You actually appear to have a triangle waveform.

I simulated the same circuit using the Pulsonix SPICE simulator and got a similar triangle waveform:

http://www.leonheller.com/psx/Integrator-graph.png

You should be able to try it for yourself using the Pulsonix demo: 

http://www.pulsonix.com/index.asp

My Pulsonix schematic is here:

http://www.leonheller.com/psx/Integrator.sch