I'm trying to convert an autocad drawing into a bitmap, that has better resolution than a simple screen capture.
You'll need a program that understands DWG format and allows print.
A search for "free dwg viewer" turned up a few. This one from Infograph was first on the list, though the print option doesn't appear to be available on the free version.
This one from Tucows is labelled as free and supports printing.
Though you might struggle to find one that does high resolution prints unless you pay quite a bit.
Sorry it this comes up short and out of date, but you didn't say if you actually have AutoCad, and I haven't for a while, but when I did it seemed like there was an option to export to postscript and then I used Ghostview to convert to whatever raster format I wanted. Also if there isn't a postscript out option any more you could always use something like PDFCreator then take that into Gsview. But in the end I'm almost always going to use Ghostscript (command line) or Ghostview (gui) to make the really Hi-res images of almost anything.