To do that so you need software to make the bootable pen drive there are many software but we recommend these software given below.
1. WinToFlash Download Now...
2. Xboot Download Now...
We are using WinToFlash for making the bootable USB pen drive.
Step 1. Insert you USB Pen Drive in your system and format it.
Step 2. Open WinToFlash.
Step 3. Now go to advance mode and select the operating system (we are using Windows XP).
Step 4. Click on Run.
Step 5. Select the source drive in Windows Source Path (where you operating system files are stored).
Step 6. Select the USB Drive.