http://code.google.com/p/exfat/

sudo apt-get install subversion scons libfuse-dev gcc
cd ~
svn co http://exfat.googlecode.com/svn/trunk/ exfat-read-only
cd exfat-read-only
scons
sudo scons install
cd ..
rm -rf exfat-read-only
sudo mkdir [mountpoint]
sudo mount -t exfat-fuse [device_path] [mountpoint]

Replace [device_path] with the device path to your exfat partition, for example: /dev/sdb1. Replace [mountpoint] with the path to your mount point, for example: /media/disk