Okay to start off, I don't think it's right to call you a 'noob'
everyone starts out somewhere right?
Anyway getting to the point..as long as your PC has a PCI-E 16x slot, any card will fit in it. So you were right, and your brother was wrong.
Also, if you get a new PSU, any GPU you put into your computer will work! So you were right about this as well.
Now if you're only going to be watching Hulu and Netflix...I think something like a GT 450 would do the trick, maybe something a bit lower if you won't really do any gaming.