No there is no need to fill out the Dell form on eBay, you just simply buy it. You can buy the DVDs from eBay even if you don't own a Dell system (theres just little point). You can only use it with a system that has a Dell Windows 7 Professional COA or a Dell system that came with Windows 8 Professional and as a Windows 8 Professional product key in the BIOS. You can just purchase the DVD on eBay I bought one the other day from ebay.co.uk The DVD I bought is good as the .iso image of it is identical in size to the Windows 7 Home Premium with Service Pack 1 DVD I got with one of the Optiplex 790s we have in the lab.  
Hi Gang I just picked up a new 790 Mini Tower loaded with Windows 7 Professional. I'd like to create a restore disc since Dell no longer provides back up OS. It's my unstanding this restore disc will provide the OS only, not the drivers. For those I'd have to go to the Dell Support site. Can someone help guide me as to how to create a restore OS disc? OR Perhaps I'll buy a Microsoft Genuine RETAIL version Windows 7, and strip the new Hard Drive, eliminating all the garbage  - start from scratch, and download the chipset, and other drivers from the  Dell Support site. Thanx Mike
Creating Restore Disc Windows 7 Pro (With an Optiplex 790)