Probably a very simple method to check is to take the left side cover off your PC and check if you can see a thin red cable going from your hard drive to the motherboard. If instead you see a wide gray ribbon cable going from the hard drive to the motherboard, then your hard drive is an IDE drive.
One other method to check is when you turn on your PC to see if you can spot the mention of a SATA hard drive on the initial bios screens within the first few seconds of being powered on. If your PC shows a full screen logo or image when powered on, you may need to press 'ESC' or 'Tab' to hide the logo and show the initial diagnostic info. The majority of PCs with onboard SATA or a SATA PCI card will show a screen listing SATA devices for a second or two during bootup.