WHY CAN'T I PLAY GTA IV ON MY MAC OS X?

Well i downloaded GTA 4 from piratebay and everytime i open it up and click on start game. it just keeps on loading at the character poster screens and stuff. then i eventually just cancel the game out, because if i don't it will freeze my MAC. My specs are: Yeah, so i downloaded it off the Piratebay.org, and I Can Start it up, but the loading screen just goes on forever and doesn't stop until the music runs out, and then i close it.. my specs are: Processor: 3.06 Ghz Intel Core i3 memory 4 GB 1333 MHz DDR3 Chipset Model:ATI Radeon HD 4670 Type:GPU Bus:PCIe PCIe Lane Width:x16 VRAM (Total):256 MB Vendor:ATI (0x1002) Device ID:0x9488 Revision ID:0x0000 ROM Revision:113-B8030H-114 EFI Driver Version:01.00.403 Displays: iMac: Resolution:1920 x 1080 Pixel Depth:32-Bit Color (ARGB8888) Main Display:Yes Mirror:Off Online:Yes Built-In:Yes Connection Type:DisplayPort Display Connector: Status:No Display Connected