When you choose the Custom option during installation, you install a new copy of Windows on your PC.
Formatting your hard disk during Windows 7 installation isn't necessary. If you want to format your hard disk, and you're using an upgrade version of Windows 7, don't use a program from another software manufacturer to reformat your hard disk prior to installing Windows 7. Instead, start your PC using the Windows 7 upgrade installation disc or a USB flash drive, click Custom (advanced), and then click Drive options (advanced).
Connect your PC to the Internet so you can get installation updates during the installation process. (If you don't have an Internet connection, you can still install Windows 7.)
Update your antivirus program, run it, and then turn it off. After you install Windows 7, remember to turn the antivirus program back on, or install new antivirus software that works with Windows 7.
If you have a Windows 7 installation package, choose either the 32-bit or 64-bit Windows 7 installation disc, depending on whether you want to install the 32-bit or 64-bit version of Windows 7.
If you want to install a 64-bit version of Windows 7 on a PC running a 32-bit version of Windows XP, follow the instructions in "To install a 64-bit version of Windows 7 on a computer running a 32-bit version of Windows XP" at the bottom of the page. For more information, see 32-bit and 64-bit Windows: frequently asked questions.
Find your 25-character Windows product key. You can find it on the installation disc holder inside the Windows package—or in a confirmation e‑mail if you purchased and downloaded Windows 7 online.
With your computer on and Windows XP running, do one of the following:
If you've downloaded Windows 7, browse to the installation file you downloaded, and then double-click it (often identified as an Application file under the Type column).
If you have a Windows 7 installation disc, insert the disc into your computer. Setup should start automatically. If it doesn't, click Start, click My Computer, open the Windows 7 installation disc on your DVD drive, and then double-click setup.exe.
If you've downloaded Windows 7 installation files onto a USB flash drive, insert the drive into your computer. Setup should start automatically. If it doesn't, click the Start button, click Computer, double-click the drive, and then double-click setup.exe.
On the Install Windows page, click Install now.
On the Get important updates for installation page, we recommend getting the latest updates to help ensure a successful installation, and to help protect your computer against security threats. Your computer will need to be connected to the Internet during Windows 7 installation to get these updates.
On the Please read the license terms page, if you accept the license terms, click I accept the license terms, and then click Next.
On the Which type of installation do you want? page, click Custom.
Choose the partition containing Windows XP (this is often the computer's C: drive), and then click Next. (Do not select your external USB hard drive.)
In the Windows.old dialog box, click OK.
Follow the instructions to finish installing Windows 7, which include naming your computer and setting up an initial user account. You can use the same names that you used in Windows XP, or choose new ones.
Insert the Windows 7 installation disc or USB flash drive, and then turn off your computer.
Restart your computer.
Press any key when prompted, and then follow the instructions that appear.
On the Install Windows page, enter your language and other preferences, and then click Next.
If the Install Windows page doesn't appear, and you're not asked to press any key, you might need to change some system settings. To learn how to do this, see Start your computer from a Windows 7 installation disc or USB flash drive.
Next: Move your files and settings back to your computer.
If an error message states that Windows can't be installed to the partition you chose, and Show details reveals a dialog box that says "Windows must be installed to a partition formatted as NTFS," then your computer's hard disk is likely formatted using the older FAT32 file system.
Cancel the Windows 7 installation, and remove the installation disc or USB flash drive.
Click Start, point to All Programs, point to Accessories, right-click Command Prompt, and then click Run as….
Select The following user, choose a user with administrator permissions, type the password, and then click OK.
At the command prompt, carefully type convert <drive>: /fs:ntfs where <drive> is the letter associated with your Windows XP installation. For example, if Windows XP is on your C: drive, type convert c: /fs:ntfs when you type, be sure to include a space immediately before /fs:ntfs.
Press Enter.
When asked if you would you like to force a dismount on this volume, type Y, and then press Enter.
When asked if you want to schedule the drive to be converted the next time the system restarts, type Y, and then press Enter.
Close the Command Prompt window.
Click Start, click Turn Off Computer, and then click Turn Off. (You need to shut down the computer completely rather than simply clicking Restart.)
Turn on your computer. Windows will proceed to convert the hard disk to NTFS and then restart your computer. Do not use your computer during this time.
When Windows XP starts again, return to step 2 under Perform a Custom installation of Windows 7.
XPS
PDF
Installing Windows 7 on a netbook
Windows 7 Upgrade Advisor
Getting started with Windows 7
Know what works: Windows 7 Compatibility Center
