No one?
You can't use old Vista keys on win7 or win8.
However:
If you want to update to win7, it can be done from within Vista itself.
You will, off cause, need a win7 media with a valid win7 key.
You cannot upgrade from Vista to win8.
There you will need to do a socalled "Clean Install". This means migrating your documents etc. via a usb stick or external harddrive.
This can be done fairly painlessly with Windows Easy Transfer which you can find on the Microsoft downloads site. Just make sure you get the version which fits your current OS and bit-system (32 or 64 bit). Once you've installed win8, you simply use the Easy Transfer for that system to tranfer your backup files back. You will need to re-install all of your apps, though.
If you run windows 7 and want to upgrade to windows 8, it can be done by using the compability tool for win8, also found on Microsoft. Be aware that this can be a lengthy process.
You can choose to save your docs etc. during this process, but will have to reinstall your apps. You will, in one of the last steps, be able to buy your version of 8.1 directly online. The tool will then download win8.1 for you (warning: This will strain your internet connection) and you will be suplied with the right keys through an email.
If you upgrade to the normal 8 on DVD, there's also an option to save your apps.
NOTE;WARNING:HEED MY ADVICE: IF YOU UPGRADE TO ANY OTHER VERSION OF WINDOWS, MAKE SURE YOU BACKUP AS WELL AS TRANSFER YOUR DATA TO MAKE SURE NOTHING BAD HAPPENS.
I haven't seen a problem yet, but this is a belt and suspenders situation: Wear both just in case.
XP users will need to run a clean install on both win7 and win8.
For those interested, here's some hardware demands for 7 and 8:
Windows 7:
1 ghz processor (32 or 64 bit)
1 Gb ram (officially anyway, but I recommend 2 GB, particulary if you plan on running XP mode)
40 gb hd with at least 15 gb free
GFX with directx 9 support, has Windows Display Driver Model driver, Pixel shader 2, 32 bits color and minimum 128 mb ram.
Windows 8:
Basicly the same as 7, but with 20 gb free on harddrive.
A note on XP mode: Officially you'll need a win7 professionel as minimum to run this. You can run it on Home Premium, but be aware that it might crash on you at the oddest times.
XP mode was discontinued in win8, but if you search the net, there are several fairly easy Howtos on setting up something that works just as well on this platform. It will take time to setup and, unlike xp-mode in win7, requires a valid xp key since you'll be setting up a virtual machine.