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There is no information about what systems will be able to upgrade to OS X Mavericks, but it looks like you will only need a Mac with the Mac App Store, so you can upgrade from OS X 10.6.8 without any problem.
OS X Mavericks is planned to be launched in fall and will include new features > http://www.apple.com/osx/preview
Lion is over 2 years old, so you probably meant Mountain Lion.
In any case, if your Mac meets the technical requirements for Mountain Lion, you'll need to check that, it will most likely meet the requirements of Mavericks. Then you should wait for Mavericks.
Mountain Lion tech specs: http://www.apple.com/osx/specs/