Until you supply exactly what OS is being installed, stick with 120GB and smaller drives.
As to the fan, you either find out why it's loud or replace it.
I have Acer aspire 3000.
1. I am thinking about replacing the original 40 GB harddrive. What are the type of harddirve that will fit for it? (will this work?) and how easy is it for me to replace the harddrive myself.
2. the fan noise is really loud. any way to decrease the noise? (i tried the compressed air and no success)