Is it possible to develop using the Android SDK on a 64-bit linux machine. The available SDK downloads seem to be just for 32-bit versions of Linux.
Yes, it is. You need to install the ia32 libraries. Check out the Ubuntu Linux troubleshooting section.
apt-get install ia32-libs apt-get install sun-java6-jdk
On (K)Ubuntu you need following 32-bit packages:
sudo apt-get install libstdc++6:i386 libgcc1:i386 zlib1g:i386 libncurses5:i386
for running the emulator you need that additional package:
sudo apt-get install libsdl1.2debian:i386