As notaloser explained, fonts are all about design and client-side stuff, so PHP has no control over that. This topic'll probably get moved down to ClientSide Technologies as the question you're asking really deals with HTML/CSS.
In reply to your problem, however, you can't use a .ttf file on your webserver to make a client understand the font. You can use PHP's GD library to generate an image with the font if you specify the .ttf file, I believe, but other than that (and some WEFT thing Microsoft makes - I don't really even think this is a suggestion, I never got it to work properly) the user must already have the font on his/her computer.
While Trebuchet MS is not listed on the page, you can visit this link to see how to use different font "faces" via HTML (though I don't believe it's XHTML compliant! :p).