Artiss Social Share (formally Artiss Facebook Link and Simple Twitter Link) will generate a URL that allows you to quickly and easily share a post or
It has been tested and been found valid from PHP 4 upwards.
Please note, however, that the minimum for WordPress is now PHP 5.2.4. Even though this plugin supports a lower version, I am not coding specifically to achieve this - therefore this minimum may change in the future.
I maintain backwards compatibility, so it should - if not, let me know and I'll get it fixed.