[andrewf]

I'll second the suggestion to attack one problem at a time. A very long time ago I was on a team that built a desktop application in Qt + Visual C++ for Windows (98/ME/2K/XP), and we wanted to port it to Mac OS X (10.3) on PowerPC.

First, we addressed the compiler issue, getting it to build with GCC instead of VC++ on Windows. This was the most time-consuming step.

Second, we built on Linux x86 with GCC, because we were quite familiar with it, and this enabled..

Third, we built on Linux PowerPC with gcc, which was the little -> big endian step.

Finally, we got it running on OS X.

For your issue in particular, I'd try to stick with 32-bit x86 over x86-64 to start, and inch my way through newer Debian and gcc versions. You could install gcc-4.2 as late as Debian 5, I think.