How to prevent the text on a website from changing on different machines?

[Duncan]

"How can I force the use of a particular font and formatting for all users"

That is you answer. You need to declare which font you want to use for the page and how it will be presented....

http://www.w3.org/TR/CSS2/fonts.html


Typography is a subject to study on its own beyond web site design...

http://webtypography.net


Be aware that the user can still use their own stylesheet which will override anything that you do and if you are messing with people's computers dictating what font they must use etc. you should give them plenty of options to change the font size, font colour and background colour etc. to meet their own requirements - old age/ poor eye sight etc.