As I understand it, you can rebuild the kernel with a certain module
enabled, and get access to >4Mb RAM in a 32-bit system. Don't recall
what that module is, though ...

As far as issues with 64-bit versions is concerned, it was my
understanding that the biggest issues would be with drivers, rather
than [app] software - especially with the closed-source video card
drivers. Have these issues now been sorted out?