And lastly, can you find this throw windows xp sp2?
If your motherboard is fairly new it'll support 8x more than likely. If it's kind of old, you don't need a serial number, just know what model your motherboard is and hit up the manufacturer website and see what kind of features. If it's running with a Ti4400 right now I believe you have 8x. If you right click on your desktop, go to properties, then click the settings tab, then click ADVANCED towards the bottom, and you should see your graphic card name on a TAB in there. Click that TAB and it'll tell you if it's running at 4x or 8x, but I'm pretty sure it's 8x although it's been a while since viewing that card. Just see what it says and if it says 8x then theres your answer
Welcome to the forums and good luck