The 3020's are suppose to be windows 8 machines but come with window 7 downgrade's and usually have windows 7 installed when they get to you. They do NOT have Product stickers with them since they are activated though the BIOS.
The Optiplex's should also come with Recovery DVD's. They are Windows 8 though and not Windows 7. If you want the Dell OEM Windows 7 ISO you can get it from my pesonal site here. You have to download all the files, then extract the ISO then burn it to a DVD (need a Dual Layer DVD 8.5GB or use a program like ISOtoUSB to boot off a thumb drive (8GB or bigger needed)
http://ttz123.com/files/Windows/
And then go here to download drivers
http://www.dell.com/support/home/us/en/19/product-support/product/optiplex-9020-desktop/drivers
Get the drivers first as Windows 7 does not have the Network drivers built into it. The driver you will need are
Chipset (All of them)
Network (Intel) and if you have wireless which they don't normally come with but if you do then the Dell 1540 Wifi drivers
Video - The Intel HD if all you have is onboard video
If you want windows 8.1 Let me know. I have those disk to that I can upload.