There are many ways to mount HDFS as standard file system, the guide and reviews can be found at MountableHDFS wiki page.
I started with WEBDAV and DAVFS and it was working quite well until my data exploded to 1Gb, the performance was getting slow and it took me more than 5 minutes for a `ls` command from root directory.
Fuse-dfs is my second try and it seems to be the best choice since it’s provided along with Hadoop package.
Compiling Fuse-dfs is impossible on Hadoop 0.18.3 because of the conflict between libhdfs and fuse library, so I tried with the latest stable version of Hadoop (0.20.1). If the guide from MountableHDFS Wiki page doesn’t work with you (which happens in most cases), these steps should be helpful:

  1. Download and extract Hadoop 0.20.1:

$ wget http://www.apache.org/dist/hadoop/core/hadoop-0.20.1/hadoop-0.20.1.tar.gz
$ tar xvzf hadoop-0.20.1.tar.gz

  1. Download and extract Apache Ant 1.7.1 if you have an older version:

$ wget http://www.apache.org/dist/ant/binaries/apache-ant-1.7.1-bin.tar.gz
$ tar xvzf apache-ant-1.7.1-bin.tar.gz

Don’t forget to add the bin directory of Apache Ant that you’ve just downloaded to your PATH variable.

  1. Set your JAVA_HOME variable if you hadn’t :

$ set JAVA_HOME = /usr/java/jdk1.6.0_16

  1. Switch to hadoop directory and start compiling libhdfs :

[hadoop@localhost hadoop-0.20.1] $ ant compile-c++-libhdfs -Dislibhdfs=1
[hadoop@localhost hadoop-0.20.1] $ mkdir build/libhdfs
[hadoop@localhost hadoop-0.20.1] $ cp -r /tmp/hadoop-0.20.1/build/c++/Linux-i386-32/lib/* build/libhdfs/
[hadoop@localhost hadoop-0.20.1] $ ant compile-contrib -Dislibhdfs=1 -Dfusedfs=1 -Dlibhdfs-fuse=1

Now you had successful compiled fuse-dfs, to mount HDFS using this library and understand current known issues, please refer to Mountable Wiki page.