i got mine from purely h20 off one of their ebay auctions, got it a little cheaper. we're really pleased with it. i have an ATO water reservoir, with a bulkhead at the bottom with vinyl tubing to make saltwater and kalk top off water in 5 g buckets. we also use the filter system (a different tube) to fill a 4g spigot jug that we keep in the fridge. we use 5 stage with DI. a last stage carbon filter is used for drinking water (like in the post below) but for us we don't feel the need for it, our water tastes great as far as we're concerned, but we do have heavily treated water here which is pretty clean to begin with.
you might want to try something like this... they have an included boosterpump, which is really cool. maybe they could swap out the drinking water tank stuff for a DI chamber, ATO float bulkhead and a waste water saddle valve thingy. this particular one shouldnt be used for huge amounts of water, just as they say in the listing. like 25g daily, which i think is good for lots of systems.
http://cgi.ebay.com/WaterGeneral-RO-Reverse-Osmosis-System-w-Booster-Pump_W0QQitemZ350044834480QQihZ022QQcategoryZ20684QQtcZphotoQQcmdZViewItemQQ_trksidZp1713.m153.l1262
as for filters, you'll probably want to shop around. keep in mind you should change filters 6-12 months depending on things like your water quality and you can also replace the poly sediment more often (6 months) and the other filters maybe 8-12 months. very fine filters will need changing more often, too. you may need or want that but as long as the water coming out has zero tds..... you'll want a TDS meter too, and a pressure gauge incorporated in the system.
for effective use of the system you should have at least 35psi but upwards of 60psi is better; i think most people should be using a booster pump (myself included) if there's not enough pressure then it'll take forever to make water and you'll waste a huge amount of water. note that if you don't change your filters often enough your psi will go down
