...the items you have at your disposal.. The actual hard drive "hardware" reinstall is easy.. Depending on the model, (which you didn't give us), unscrew, or slide out the old hard drive after unplugging it from the wiring inside, then plug in the new one and slide in or screw the cover back on..
And yes, the operating system plus all drivers and software will need to be reinstalled on the new hard drive.. If you're lucky enough to have been given a set of recovery discs, or wise enough to have creating such discs using the recovery disc creation tool on Gateway machines, then the reinstall should be fairly simple.. After backing up all your important documents on the existing setup, remove the old hard drive, replace with the new hard drive, then boot from the first recovery disc.. (As long as the system is set to boot from the DVD/CD drive first, then disc will automatically boot at start up. If the system is not set to boot at startup, then you need to access the BIOS settings and change the boot order so it boots from the DVD/CD drive first.) Once the first recovery disc starts up, you follow the prompts to create a new partition on the drive, format the drive, then reinstall the operating system and all the other stuff as well. Much of these steps are automatic as long as the recovery discs are specifically created for your computer.
If you don't have recovery discs, then you'll want to contact Gateway and obtain them.. Generally, computer manufacturers will provide such discs at a fairly inexpensive price.
If you don't have, or can't get, recovery discs for you computer, it gets a lot more difficult.. First, you have to purchase a new operating system installation DVD/CD.. The cost depends on where you buy it and which version you need.. Think $100 - $200.. Next, you'll need to obtain all of the driver installers BEFORE in attempting the reinstall, then burn them to a CD for use after the operating system is on the machine... You probably can find the drivers at the Gateway site, but if you're wanting to install an operating system which is different from the original model, it can get problematic as to whether such exist. Finding the correct driver isn't always and easy task. (Writing down all the device types, device manufacturers, and driver versions from "Device Manager" is a good step to help you find those drivers later.) And after that, you'll need to find all the various software titles you want to install for your personal enjoyment.
Hope this helps.
I was recently given a gateway laptop with a crashed hard drive(?). My funds are extremely limited so I thought about replacing this myself. I looked online and found a compatable one at sparepartswarehouse.com for around $50 which I can do. MY question is how difficult is this? and do I have to reinstall the operating system. If so, how?