Planting boxes for flowers

I have decided to make some raised planting boxes rather than go into the earth, which here is a combination of sand dune sand and caliche. I believe that some treated lumber would last the longest, or perhaps some railroad ties. Maybe some old building beams if I can find them for a decent price.
Is there a danger of the chemicals leaching out from treated lumber or railroad ties for garden beds? What if I put a liner? I intend on going to the nursery, and getting a really good mix of soil delivered, or maybe just getting some bales of peat moss, and some bags of soil and mixing. But I don't want to do all the work and spend all the money if I am planting these things in a toxic box.
TIA
Steve
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sand dune sand and caliche.
Southwest?

I read this question alot here. Here are a couple links to help you make a decision :
http://www.ecologycenter.org/factsheets/pressure-treated_wood.html
http://www.naturalhandyman.com/iip/infxtra/infpre.html
Creosote: http://waterquality.montana.edu/docs/wqfaqarchives/wq_faq_3.shtml
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On Thu, 28 May 2009 10:23:42 -0600, SteveB wrote:

It shouldn't matter for flowers, you aren't going to eat them. If you are growing food then you absolutely don't want to use any sort of treated lumber.
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