HTML support for math formula layout is pretty pathetic, and everybody struggles with it. You inherit the problems when you try to copy and paste HTML formulae into Word, so explaining it from that perspective may shed some light on the problem (though not a solution, I'm afraid).

The font is only part of the problem, though it's a biggie: You can only count on any given computer having a serif (Times), sanserif (Helvetica or Arial), or monospaced (Courier) font. There's no guarantee that a particular symbol font will be present. Even a symbol font helps only so far--you also have to deal with large symbols that span multiple rows, such as braces, the integral sign, and the root symbol; and you need to deal with the complex layout of nested equations. There's no natural way for a text system like HTML or Word to deal with those very large characters, so those are prime candidates for using images instead. This leads to the phenemonen you see where you get a mixture of symbols and images.

There's a new standard for displaying mathematical formulae on a Web page called MathML that aims to solve the problem. Unfortunately, at the present time it only works on the Mozilla browsers, e.g. FireFox.

One alternative I've seen is to use a programming-like notation for math formulae. For example, if you can't superscript, you can write an exponent as x^2 to indicate "X squared". Division is represented by a slash separating two numbers on a single line, asterisk for multiplication, etc. Since most languages have math functions, you can express things like square root as a function call: sqrt(N). Not a very satisfying solution, is it?

I'm afraid you're kinda hosed, Daniel.