This font very similar to Arial but it's not, what is it?

I need to create a new button to add on my website's menu. I need to use the same font the designer used so the new button looks like the others. The menu buttons have text in the bottom. It looks a lot like Arial but it's not. The website is http://reseaubio.org. If someone can identify the font I would be grateful.

Comments

Here are the images;

Most of text looks like http://Tahoma Microsoft font but "Petites annonces" is set in a different font, I don't know what it is.

Verdana might be closer. "Petites annonces" is probably Arial, and "Liste des abonnés" looks more like Lucida Sans/Grande.