You would need to set up a separate server to act as the boot source... far too much work to set up this way, and unless you have the proper networking hardware (i.e. a Gigabit link all the way through between your PXE server and the target system you are deploying Windows to), it's faster to install from an optical drive.
Beyond that, it's actually faster to install from a usb flash drive (as opposed to an optical drive) anyway. If you have an ISO file of your Windows 7 dvd handy, you can use the Windows 7 USB/DVD Download Tool (found at http://store.microsoft.com/Help/ISO-Tool)
to create a bootable flash drive. The target flash drive must be at least 4GB in size.