Attached are binary of the tools to run on Linux PC and root fs from buildroot. You can use it to compile kernel and apps.

Login as a user account on Linux PC, eg, hippo. The user home dir will be /home/hippo, short form as ~/ .

Use web browser to download the cross tools (69MB). Best thanks to Altera's kindly hosting these files. (but don't use Windows ftp, it corrupt the files)
(sha1sum 6873249d8eae7c2981aac6791f044ddaab507566  nios2gcc-20080203.tar.bz2)
Open a terminal. Run as root or use sudo,
sudo tar jxf nios2gcc-20080203.tar.bz2 -C /

The cross gcc tools was expected to be installed in /opt/nios2 dir. But you may install in any other dirs. Then setup the PATH for the cross gcc, you can add a line at the end of file ~/.bash_profile (or ~/.profile on Debian/Ubuntu) ( the file is hidden, you have to use "ls -a" to find it . For "gedit" use open Location, and enter the file name)

PATH=$PATH:/opt/nios2/bin

After you change the .bash_profile or .profile, you need to logout and login again. So that it will be in the PATH when you login.

Check with,
echo $PATH
It should display like this, with nios2 path at the end,
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/opt/nios2/bin

To verify the cross gcc, try out,
nios2-linux-uclibc-gcc -v
It should display the info,
Reading specs from /opt/nios2/lib/gcc/nios2-linux-uclibc/3.4.6/specs
Configured with: /root/buildroot/toolchain_build_nios2/gcc-3.4.6/configure --prefix=/opt/nios2 --build=i386-pc-linux-gnu --host=i386-pc-linux-gnu --target=nios2-linux-uclibc --enable-languages=c --enable-shared --disable-__cxa_atexit --enable-target-optspace --with-gnu-ld --disable-nls --enable-threads --disable-multilib --enable-cxx-flags=-static
Thread model: posix
gcc version 3.4.6

Then try build kernel and apps as in the UClinuxDist .

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Optionally, you can install ccache, the compiler cache, which can reduce the compilation time a lot.
Install required package, as root or via sudo
On Fedora,RHEL, 
yum install ccache
On Debian/Ubuntu, (via sudo)
apt-get install ccache

Then add links, still as root or via sudo
ln -s /usr/bin/ccache /usr/lib/ccache/nios2-linux-uclibc-gcc
ln -s /usr/bin/ccache /usr/lib/ccache/nios2-linux-uclibc-g++
ln -s /usr/bin/ccache /usr/lib/ccache/nios2-linux-uclibc-c++

When you compile something, the cache will be used, you can check cache status with,
ccache -s