I've very basic understanding of linux systems, but I've a server which was setup a while ago to host some web apps. Recently I decided to test out and implement Sphinx but unfortunately I cant get the install to work.

I'm running a Debian Lenny distro and when I try to install sphinx it says -

checking MySQL include files... configure: error: missing include files.

******************************************************************************
ERROR: cannot find MySQL include files.

Check that you do have MySQL include files installed.
The package name is typically 'mysql-devel'.

If include files are installed on your system, but you are still getting
this message, you should do one of the following:

1) either specify includes location explicitly, using --with-mysql-includes;
2) or specify MySQL installation root location explicitly, using --with-mysql;
3) or make sure that the path to 'mysql_config' program is listed in
   your PATH environment variable.

To disable MySQL support, use --without-mysql option.
******************************************************************************

I do have mysql 5.1 installed but I can't find the include files, AND one more thing.. I read around the net that I probably need libmysqlclient15-dev but when I try to install that using apt-get i receive the following error.

The following packages were automatically installed and are no longer required:
  libxcb-aux0 libts-0.0-0 libxcb-atom1 ttf-dejavu-extra hunspell-en-us g++-4.3
  libmysql++3 libnspr4-0d libdirectfb-1.0-0 libxcb-event1 libasound2
  libstdc++6-4.3-dev libhunspell-1.2-0 ttf-dejavu libmozjs2d
  conkeror-spawn-process-helper libnss3-1d
Use 'apt-get autoremove' to remove them.
The following NEW packages will be installed:
  libmysqlclient15-dev
0 upgraded, 1 newly installed, 0 to remove and 276 not upgraded.
Need to get 7590 kB of archives.
After this operation, 26.3 MB of additional disk space will be used.
WARNING: The following packages cannot be authenticated!
  libmysqlclient15-dev
Install these packages without verification [y/N]? Y
Err http://ftp.us.debian.org/debian/ lenny/main libmysqlclient15-dev amd64 5.0.51a-24+lenny5
  404  Not Found [IP: 35.9.37.225 80]
Err http://security.debian.org/ lenny/updates/main libmysqlclient15-dev amd64 5.0.51a-24+lenny5
  404  Not Found [IP: 149.20.20.6 80]
Failed to fetch http://security.debian.org/pool/updates/main/m/mysql-dfsg-5.0/libmysqlclient15-dev_5.0.51a-24+lenny5_amd64.deb  404  Not Found [IP: 149.20.20.6 80]
E: Unable to fetch some archives, maybe run apt-get update or try with --fix-missing?

Can you help me out by suggesting how to install the required packages and run the Sphinx.