You can still use Vista, Just use the Pale Moon browser.
It's asinine to think that just because a Comp can't get so-called security updates it immediately invalidates your machine. I have never updated my computers and I NEVER got a virus. And I know for a FACT being a member at plenty of other computer forums that people still get malware even though they let M$ monkey with their machine with updates. Especailly not turning off M$ updates to drivers. That's a HUGE mistake right there.
Now how on earth do I not have malware you may ask? Because I don't browse and us my computer like an inept clown. I also use safeguards. VooDoo Shield Beta, Sandboxie, NoScript and Imunet or Bitdefendewr Free.
But I digress. Since your primary use of this laptop is office orientated and Internet related, you could install Linux Mint. That would be a huge upgrade in terms of keeping your computer secure. In fact, you wouldn't really even have to use any anti virus. Well, you could install Imunet just as a feel good felling, but it is really not needed as Linux gets very few viruses. Not saying they don't exist, but it's out of the scope.
Just some food for thought. I will now prepare to be ridiculed by the lords of M$.