Several Computer questions for those who know what there doing.?

First i have Windows XP Media center i run Internet explorer i do have chrome from Google but don't know how to make it my main thing instead of Internet explorer cause on internet explorer i get on a lot of sights "invalid argument" all the time as a pop up and i "hate" that and don't know how to make it stop, how do i make Google chrome my main browser and please go "Step by step" but on some sights that "annoying" pop up "invalid argument" still pops up on Chrome also what do i do to make that stop thanks. Oh if it matters i got me a old Dell computer desk top.