I have an acer laptop, as soon as I got home I made a driver disk, formatted the hard drive and downloaded Windows Vista Lite off of BT. DL the same version of windows you have now, ROM/Retail, and use your windows key that came with your Acer, then activate. It will work fine and you are not doing anything illegal as you are using your legal key on the same version of the software. That is what I would suggest. Sped mine up about 30% too.
Vista lite is great, it is only about 300 MB and is fast as shit. I also partitioned my HDD. ]
DBAN is free and will format your hard drive for you. Once it does it there is no getting the info back though.