First, if the file is a ZIP file, you need a program to unzip it. PKZip was the first of these and there is one called WinZip that also does a good job. I use Magelian which is a file management program and it will handle the zip files with ease.

As for a viewer, after you get the file unziped, the open an individual DXF file with most any Cad program. The free cad viewer is one example, but having looked at a lot of these "free plans" few if any are really ready to start building with. I've been using Rhino3d for a few years now and it will read most of these files. None that I saw would allow you to start cutting parts and have a set of plans that you could build from.

If you can get a clean DXF file, some blue print shops will print from a file for you. Probably at about the same cost as buying a proper set of plans.

For printing at home, you need an inkjet that will print from roll paper. Epson made a few different ones a few years back, the stylus Photo 870 and the photo 1270/1280 are a couple the first can pring 8 1/2" wide rol paper up to 120 inches long. THe 1270/1280 printers can print up to 13" wide and again up to 120 inches long. Youe CAD software has to support that though. Botom line, purchasing a set of plans with the manual for $20 or so is very good value. I have both of the printers above and the Roll paper cost about $0.50 a foot and we all know how much ink cost. I just printed out a set of ribs and main spars for a Ruperts Dad to day and I chewed up about 18ft of paper. $9.00 down the drain without ink or the cost of the software and I don't have the plans printed for assembly, just parts to cut.

Free usually isn't.

Don