There are a couple of ways you can do it..
The first and easiest, would be- If the Dell didn't come with a disk, call Dell and have your laptop handy to give them your serial, and they will mail you the install disk.
If they don't and you don't want to wait, you can always download an .ISO.. Follow these instructions for USBhttp://answers.microsoft.com/en-us/windows/forum/windows_7-windows_install/how-to-install-windows-7-on-a-netbook-from-usb/ff8f440f-b956-4d82-8d8b-b42ff64115d9
and here to make the ISO multiboot so you can have starter..http://www.mydigitallife.info/how-to-select-any-edition-or-version-sku-of-windows-7-to-install-from-single-edition-dvd-disc-media-or-iso/
I would still try and get the disk from Dell, it would be your best bet..