I used QCad v2 on Linux when I designed my travel trailer and it worked fairly well to do 2D layouts. Version 3 took a huge step backwards in terms of usability and reliability for me, though. Now that I am in the process of designing a workshop I am taking the time to learn openscad which I think will serve me much better in the long run even though the learning curve is pretty steep.
https://mega.nz/#!8dRklKwB!wQMyNONxadKLppMQYl2FatiwcfzkZ_lKzb2SI0etVIc
So this file has my drawings as well as some drawings i found online which might help with designing ATX motherboards in CAD. Let me know if there's any issues downloading it!
Also, just a shout out to "QCAD" who make a free CAD tool which is what I've used for the design. http://www.qcad.org/en/ Cross platform to!
With Zero CAD experience at all I was able to figure out how to use the program by just clicking around and make the attached.
Try using qcad. Setup custom page dimensions to 12" (Edit->Drawing Prefrennces->Pringing->Page) and then import all the dxf files you want on that sheet. Then arrange them and export to pdf.
What I do for my designs is downloading the DXF file for the case layers and editing them using the community edition of QCAD. Try to avoid working with SVG files for laser cutting, it gives more headaches than it's worth.
I use qcad. I have downloaded AutoCAD, Inventor, and Solidworks from torrents and installed them on VMs of XP and they work fine, but I still use qcad, it does what I need and I don't have to put up with Windows.