Since ARM lacks an FPU, you'd need to rewrite the code to integer only. There is one such project for PocketPCs (it is commercial, AFAIK - BTW I always wondered whether they bought the full license from id or if they are just plainly infringing the GPL, since I saw no code for download on their page). Anyway, one could start with PocketQuake or other ports and hack it to have an acceptable performance on the N770. I bet it is doable.