You should be fine. There is no copyright on ideas. Names\Graphics\Music etc. are protected, but not the game idea.
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Tetris is illegal in any way. Even Tris is copyrighted by them and any use of it or its princip without a license will bring you in bad problems.
Sounds a bit contradictory ---
what if a Tetris remake wasn't called anything remotely like Tetris and obviously comprising different graphics and music?
(Surely the arrangement of 4 squares cant count as copyright graphics???)
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PowerPC603 - I think you'll be fine! Only you may need to be careful with names for things like Jumpgates (Netdevil may not like it), plus don't call your spaceships the same names as those from Freelancer (never played it so I wouldnt know) etc. and you'll be okay.
I dunno if anything from 'Galactic'open-source is any help?