Note: I am also using an improvised mattress made out of eight $9 sleeping bags inserted into a zippered vinyl mattress cover to go with this DIY platform bed for a complete, inexpensive, portable, lightweight bedding solution. Details are at http://www.instructables.com/id/DIY-Mattress-Substitute-Portable-Inexpensive-L/
Step 1: Buy 12 "LACK" Side Tables from IKEA
For a queen bed, buy 12 "LACK" side tables from IKEA - http://www.ikea.com/us/en/catalog/products/20011413 ($7.99 each as of 05/26/10). Each individual piece weighs just 10 lbs and measures (as packaged) 22" W x 2.125" H x 33.125" L. Though made of particleboard and therefore extremely light, I was told each table can support the weight of one adult standing on it. I was able to load and fit all twelve packages into my subcompact car quite easily.