Windows 7 can be installled in netbook with no DVD drive using an USB key. It needs to be installed using a USB key. The USB key must have 4GB or more free storage space. In case you can do with command lines. You might use the DIskpart utility. Most of them will prefer to use the Windows 7 USB/DVD Download tool. The tool will also create a bootable DVD from which you can install the OS. That's the only solution if you have a netbook without optical drives.