Verovatno si prilikom instalacije preskocio opciju upgrade sa XP na Win7 nego si instalirao potpuno novu pa zato sad imaš dva OS. Da bi smanji vreme pojavljivanja te opcije kucaj u Windows help and suppor t „multiboot configuration” i tamo je lepo objašnjeno šta treba da uradis. Za svaki slučaj evo copy/past tog teksta

If you have more than one operating system installed on your computer, you can choose which one starts when you turn on your computer. More than one operating system installed on a computer is often called a multiboot configuration. For more information, see Install more than one operating system (multiboot).

Click to open System.

Click Advanced system settings. If you're prompted for an administrator password or confirmation, type the password or provide confirmation.

Click the Advanced tab, and then, under Startup and Recovery, click Settings.

Under System startup, in the Default operating system list, click the operating system that you want to use when you turn on or restart your computer.

To see the list of available operating systems during startup, select the Time to display list of operating systems check box. To reduce the amount of time before the default operating system starts, decrease the number of seconds shown.

To start the default operating system automatically without displaying a list of available operating systems, clear the Time to display list of operating systems check box.

Click OK, and then click OK again.