I downloaded it and put it in a folder but it didn't work, what exactly am I supposed to do?

Also, is there any chance that Bethesda will fix this stuff on their own, and I won't need it later on?

What folder?

If it was the "Wherever you installed it"\Steam\steamapps\common\fallout new vegas folder, that is the right folder.

Maybe try restarting Steam and the game.

P.S.

One can hope they do, but only time will tell.

I'm sure they will try to fix it eventually.

Refer to this thread for the fix.

http://www.gamesas.com/index.php?/topic/1123460-potential-fix-for-npc-slowdown/

You just simply paste the dll file in these locations

"C:\Program Files\Steam\steamapps\common\fallout new vegas" (Ofcourse if you installed steam somewhere else thats where steamapps will be)

and in
"Documents - My games - FalloutNV "

My os blocked it and said something that it has been blocked to protect the system files, since it came from another computer, I had to right click it and click allow it.

Dude disable UAC. Its crap