How similar can a company name be without infringement?

I came up with an idea for a company a few years ago, which I hadn't been able to start due to life circumstances. Now I find out someone beat me to the punch on the idea, with a similar name and everything.



Now I have to reinvent the idea for my company, which sucks because I really love the name. And the difference is simple yet distinguishable.



For example, how does MySpace.com and Space.com exist without infringing on each other? Because that "My" is the same difference in names between this company and the one I wanted to start.



I know the best thing would be to come up with an entirely new name but I'm curious.