Tell us about yourself!
you have to change the way your BIOS loads your OS, originally with windows installed it only looks to windows, you have to point it at ubuntu first and then it will go to GRUB which you will then use to pick windows or Ubuntu
You could start your own server and host clients websites however unless you have someone who knows how to do this sort of thing (someone with a degree in Comp Sci) I wouldn't suggest it. It wouldn't be very efficient or secure for you're clients and unless you have a ton of money you wouldn't be able to compete with the bigger server names that you named above. This post is more for personal use, If you would want to start a business doing it, I'd suggest finding someone who knows how to do this without looking at an instructable.