Differences in character size (pixels) and how to deal with them, suggestions?

So there's this problem where each and every character seems to have its own character width. You can observe this in ROBLOX, it looks somewhat like this (Wordpad replicates it well enough):

http://i.imgur.com/yHbO7St.png

-OR-

http://i.imgur.com/yHbO7St.png

My question is how can you deal w/this when you need to have several text labels each generating what seems to be random texts and you need to account for this difference in width (pixels) how would you deal with each character seeming to have its own length?

Suggestions, ideas, or how-to's are appreciated. Please help!

I'm asking for pointers on how to BEST do this.