Windows licence??

Hello, I have restored an older laptop of mine, it originally came with Windows Vista (which I liked)
I now have installed a new HDD and am contemplating my next best plan.
I do have a Windows licence for Windows Vista on this machine, unfortuately I know of no way
of getting Vista. I could use this laptop as a designated linux machine, as I do use Debian, Slackware
and try some others on occassion.
This machine is an Acer Aspire 5735-4817, 2008, 32 bit.
I am not opposed to buying a licence for Windows 7. Any suggestions for the best route to go here?
I also use Windows 7, dual-booted on another laptop with Slackware 14.1, plus a newer
laptop with Windows 10, dual-booted with Debian 8.2.
All advice appreciated. Thank you.

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