JoeGKushner
Adventurer
If you are looking to 'try out' 4th Edition, without a huge initial outlay, having a look at the up-comming D&D Essentials Starter set could be a good idea.
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Whereas the pdf version of Pathfinder might also help you try out that without spending too much either.
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These are both good points.
3.5, or at least the D&D version, should be right out the door. If you're new and you're not using a pirated copy on PDF, the core books are long out of print and the PHB is hard to find and/or expensive.
The D&D line has two dummies books and the new introduction starter set.
Pathfinder has a lot of adventure paths which can be important to someone just starting. In addition, the wisdom of selling core books like the Pathfinder rules, Bestiary, etc... for $9.99 on PDF make it easy to afford.