Windows Vista Home Premium & PS/2 Mouse and Keyboard

I have SONY Desktop model number VGC-RC110G which came with Windows XP Home about a year ago. Recently, I purchased Windows Vista Home Premium and did a clean install. Since I have limited number of USB ports on my computer, I would like to continue to use my mouse and keyboard using PS/2 port. However, when I plug in my mouse and keyboard using PS/2, they don't work at all. But when I connect them using USB, they work fine. What are the things that I need to look into to fix this problem? What type of driver should I upgrade so that I can use my mouse and keyboard using PS/2 on my SONY VGC-RC100G? Can someone please help me with this problem? Please.... I need help.