jeff powell looks ahead to saturday 's fight at the mgm grand .
floyd mayweather takes on manny pacquiao in $ 300m showdown .
both fighters arrived in las vegas on tuesday with public appearances .
read : mayweather makes official arrival ahead of manny pacquiao fight .
al haymon : the man behind mayweather who is revolutionising boxing .
mayweather vs pacquiao takes centre stage ... but who 's on the undercard ?