How to check whether the PCI slots in my PC's motherboard are PCI-E16x or not ?

Should I check through any system software ? B'coz I'm going to buy a new graphic card next month. My PC is an old one with Celeron Processor D with DDR1 RAM support. There are both AGP and PCI slots (32-bit add-on card slots).,motherboard : MSI. and SATA Hard Drives.