|A few other differences:|
-AGP is a parallel bus; PCIe is serial.
-An AGP 8x slot can send 2.1GB/s downstream; a PCIe 2.0 x16 slot has 8GB/s of downstream bandwidth.
-AGP has horrible upstream bandwidth: only 133MB/s (the same as a standard PCI slot). This makes AGP quite bad for OpenCL/CUDA/GPGPU applications. A PCIe 2.0 x16 slot has just as much upstream bandwidth as it has downstream: 8GB/s
If you're looking for a video card for your Core i3 system, you'll need a PCIe card.
Super PIII | Unlocked ES Tualatin @ 1.8GHz (150x12, 1.65v), 512K L2
3GB PC2700 | 500GB | Radeon x1950Pro | Apollo Pro 266T | Win7 Pro