Oh... in that case, and if you would like to keep using what you already know, you might want to read up on the "compatibility" feature of Microsoft's current operating systems. I was assuming you'd already looked into that and struck out. Using that feature I run some old 32 bit applications under 64 bit Windows 7 just fine. Makers of my old programs all said they would not work under 64 bit Windows, but their goal was to sell me a new version.... so they convienently didn't mention the possibility of continued use via the "compatibility" feature.
Also, have you already checked with readers at some autocad forums to see if anyone has charted these waters?
If it jams, force it. If it breaks, it needed replacing anyway!