But if I overclock and root my phone, can I download games that I couldn't download from the market from other sites? Or does the "blockage" still exist, if you know
If you go to Settings>Applications then tick 'Unknown Sources' you can download apps from sources other than the market. You dont have to root to do this.
P.s. some mobile operators disables this
p.p.s. but mine's SIM free so...