Compiling the arduino IDE in 64bit linux supposedly requires some java version juggling, but a symlink hack worked fine for me on AMD64 Ubuntu 9.10 (Karmic).
Here's roughly what I did to get rolling following david.huard's advice at http://code.google.com/p/arduino/wiki/BuildingArduino. Note that I already had a standard dev environment set up (svn, make, unzip, etc) so you might need to fulfill some more dependencies. Also, you almost certainly don't need the whole leaflabs svn repo; add trunk/ to the checkout url?
$ uname -a
Linux ziggy 2.6.31-16-generic #53-Ubuntu SMP Tue Dec 8 04:02:15 UTC 2009 x86_64 GNU/Linux
$ sudo aptitude install sun-java6-jdk gcc-avr dfu-util librxtx-java
$ svn svn checkout http://leaflabs.googlecode.com/svn/ SVN_CHECKOUT
$ svn info
Revision: 110
$ cd SVN_CHECKOUT/trunk/maple/build/linux
$ ln -s /usr/lib/jvm/java-6-sun SVN_CHECKOUT/trunk/maple/build/linux/work/java
$ ./make.sh
$ cp /usr/lib/librxtxSerial.so SVN_CHECKOUT/trunk/maple/build/linux/work/lib/
$ sudo ./run
