Using Mac OS X's built-in Boot Camp Assistant (in Applications, Utilities Folder) you can install Windows 7. After install, when you turn-on your Mac, hold the Option Key to Boot into Windows. This method runs the Operating System off it's own Partition of the internal Macintosh Hard Drive. When you boot into it, Windows will be Full-Screen, and "running natively."
An alternative is to Run Windows INSIDE Mac OS X using a Free program called "VirtualBox." This way, VirtualBox will be in your Dock on the OS X side. You will launch it, and run Windows 7 (or any Operating System) Virtually. Please note, this will be slower, and will need certain Drivers. There may be limited Functionality running Windows inside VirtualBox, instead of natively inside Boot Camp. And it lacks some of the Hardware Features available to a Native Operating System.
If there is a "problem" with your MacBookPro's Hard Drive, I would consider getting a NEW Solid-State Drive (of say, 128 GB). This can be purchased for around $100-$125. A few benefits: your Operating System and Programs will boot/launch Faster.
It may also be a good idea to move all of your Media to the External Hard Drive (noting that they will only be available when the External HD is plugged-in via USB. Go to iTunes and in Preferences tell iTunes to use the External Hard Drive for Storage.
Check your MacBookPro Model Number on Wikipedia (search MacBookPro). Make sure to Upgrade your RAM to Maximum Capacity. Then, Download whatever version of Mac OS X is the latest that machine will run. After Mac OS X Snow Leopard 10.6.8, the Mac App Store is Available. That means all versions of Mac OS X after 10.6.8 can be easily downloaded via the Mac App Store onto a New Hard Drive.
1. Purchase the latest version of Mac OS X your MacBookPro will run for $20 in the Mac App Store (let's say Mountain Lion, or Mavericks on Tuesday October 22nd)
2. Purchase an SSD (Solid-State Drive) for around $100 at 128 GB
3. Plug the SSD into the Mac's USB Port.
4. Go in Disk Utility.
5. install OS X onto the SSD using Mac OS Extended (Journaled)
6. Turn-off the MBP (afterwards)
7. Flip the MBP over and open the botttom.
8. install the New SSD that you just installed Mac OS X onto.
9. Turn-on the Computer.
10. Run Boot Camp.
11. install Windows 7 onto it's own Partition, using Disk Utility again.
12. After install, boot into Windows by holding the Option Key after hitting the Power Button to turn the Laptop on (hold it down for a few seconds).
13. Install all the Microsoft Updates and Drivers for your Printer and Peripheral Devices.
14. ReStart into Windows.
15. After all this is done, any time you turn-on your Computer, you choose which OS to boot into. You can even choose a Default in Mac System Preferences, System, StartUp Disk.