Is it possible to run two Anti Virus softwares at your PC, or will it harm your PC?

Acer Aspire x1800 Operating System * Genuine Windows Vista® Home Basic Processor * Intel® Pentium® Dual-core processor E5400 (2.7GHz, 2MB, 800FSB) Chipset * NVIDIA® GeForce® 7100 and nForce® 630i Memory * 2GB of DDR2 800 MHz SDRAM Hard drive * 320GB SATAII 7200RPM Optical drive * 16x SuperMulti with Labelflash™ technology Card reader * Multi-in-1 [...] http://bit.ly/mQKpmu