First you have to get all needed drivers downloaded and saved in an external disk/ pendrive, you can find them out here:
http://support.toshiba.com/drivers
(make sure to select correct windows version i.e. Windows 7 64 bit).
Afterwards you need to boot with the Windows 7 installation DVD and start the installation process formatting the primary partition in your laptop.
Once finished (simply follow the steps the installation wizard shows you) start installing the drivers you've downloaded from Toshiba's website, starting with chipset (INF) drivers, then LAN, wireless, Audio, graphics etc.
Finally install any software of your liking, better to install antivirus after installing all drivers, sometimes the antivirus causes conflicts when installing drivers.