Install Tidy, PHP
On Ubuntu, you can add tidy to your php5 installation by running this command in a terminal:
$ sudo apt-get install php5-tidy
If you want to check if it is already installed or validate that the command above worked:
$ php -i | grep libTidylibTidy Release => 25 March 2009 // means tidy is installed
To install both php5 and tidy at the same time, use this command (as an alternative to the "--with-tidy" configuration option):
$ sudo apt-get install php5 php5-tidy
I was having the same trouble, and wrote up my solution here:
Installing Tidy 2.0 PHP extension on Ubuntu 10.10
http://web.onassar.com/blog/2010/11/16/installing-tidy-2-0-php-extension-on-ubuntu-10-10/
It works on newer versions of Ubuntu as well.
While it may not be the most direct route, it works well.
I hope it helps others.