Do you have a USB flash drive, at least 4 GB in size.
If you do use the following free utility unetbootin to make a bootable USB flash installer
from the .iso.
UNetbootin - Homepage and Downloads
Download the version for windows.
Insert your USB flash drive and then click the unetbootin .exe you downloaded above.
Make sure the flash drive is formatted to NTFS before inserting it.
Now click the unetbootin .exe and skip the first field's (distribution) radio button.
Click the next field's (disk image) radio button and use the browse button at the far right of the field to browse to the location of your Win 7 .iso and then click OK at the bottom right.
It will take a few minutes to complete the install of the setup files to your USB flash device.
When complete shut down your computer (I'm assuming you have a netbook since you mention that you have no optical drive) and boot to the Flash drive. You may have to change the boot order in BIOS to allow booting the flash drive installer.
You should get a usable Win 7 installer.
Installing Win 7 from a USB flash drive is quicker (almost 100%) faster than installing from a DVD.