Firstly, you have not told us what Linux variant you're running.
Requiring the .so file (Shared object) just basically means you're missing a package. On a modern system like Fedora Core for instance, you have the "yum" tool, so doing "yum search php-mysql" might be what you're after
Most likely, you need php-mysql, to provide /usr/lib/php/modules/mysql.so
On my system, I have several occurances of mysql.so for perl, and python bindings as well.
[byte@albus ~]$ locate mysql.so | xargs rpm -q --whatprovides
libdbi-dbd-mysql-0.8.1a-1.2.1
perl-DBD-MySQL-3.0004-1.FC5
php-mysql-5.1.4-1
php-mysql-5.1.4-1
MySQL-python-1.2.0-3.2.2
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Colin Charles, Chief Evangelist, Monty Program Ab
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