Oh. Well then....
Text Size
As long as the forum supports BBCode (most do), this should work:
[size=25pt]LARGE[/size]
[size=5pt]small[/size]
[size=10pt]AvErAgE[/size]
Note that the above dont work because they're in a code block.
Font Type
Tahoma! Again, use the below BBCode:
[font=Tahoma]Tahoma[/font]
[font=Verdana]Verdana (our normal font)[/font]
And so on. But note that not all fonts work; there should be a list out there on the internet if you look hard enough.
So there you go. Anything else you wanted?