dell optiplex 360 to 780

Questions.    I am new to the dell community.   I also am not very up on computers as far as repairs, upgrades, and things like that, but i do have some friends that work in i.t. that can help if needed.  I just dont know much about these, so please, any info is helpful, just try not to roast me too bad, total newbie here.    Main question is, i just acquired 4 optiplex 360 towers, but the hard drives were removed due to the information on them.  How limited am i on replacement hard drive options.   If there are reliable upgrades available, does anyone know what they are??  I am looking to build at least 2 of these for personal desktops, not sure what to do with the other 2.  Just need to get one up and going to see what the performance and operation is like.   They all have windows vista stickers on them, but are they capable of possibly running at least windows 8 with upgrades??   Just asking and looking for the best system to reload onto it...