There are many ways to install windows without CD/DVD, however the best way is by creating a windows [7, vista or xp] bootable USB drive.
Creating a Windows 7 [ Vista or XP] bootable USB drive in a few easy steps.
Windows 7 ,or Vista or XP ISO
4GB+ USB Pen drive (for windows 7 or vista) or 2 GB (for windows XP)
UNetbootin tool, Download here http://unetbootin.sourceforge.net/ [...] latest.exe and save it. (is free software)
(backup any data on the USB, as it will be formatted)
Step 1: Insert USB pen drive into the USB port
Step 2: From the Start menu, go to My computer, right click on the USB drive, then select Format. In format windows, under File System choose NTFS. then click Start. Once complete close the window.
Step 3: Open the UNetbootin tool (from the location you saved it in), when the the program opens up, 'Diskimage' [in the middle] should be selected . Now click on 3 dots [...] to browse
for your Windows 7, Vista, or XP ISO image file.
Step 4: At the bottom of the Unetbootin windows , the setting should be
Type: USB Drive
Drive: for this, you choose your correct usb drive letter
Step 5: Start the process by clicking OK
Wait as the ISO is extracted to your USB drive; once is done, you will have a bootable Windows 7/Vista/XP USB drive .
Your USB drive is ready to boot and install Windows.
Remember you need to change the boot priorty in the Bios, change it to USB (from the HDD or CD ROM/DVD drive)