It appears you cannot make a LaTeX equation in the Wiki, but it may be possible, for instance to place a link to a mathematical formula.
This is available from http://www.codecogs.com/latex/eqneditor.php under the "URL encoded" format.
Also, you may be able to see a list of characters here to copy and paste at the top of mathematical documents, so that you can use them.
α β � Γ ∂ δ ε ϵ ζ η θ Θ ι κ λ Λ μ ν ξ ο ° π ρ ς σ τ υ ∩ φ Φ χ ψ ω Ω ~ ≈ ≠ ≡ ± ≤ ≥ Δ ∇ Σ ∂ ∫ ∏ → ↔ ∞ • ∙ ♠ ♣ ♥ ♦ -JonDoolin
(This does NOT work on all phpwiki's; it may be site dependent.)
You can hack WardsWiki to render this as an inline image as follows (look at the source Luke):
Note the "&a.gif" at the end. It clutters the image a bit, but tricks the wiki-engine into believing this to be an image (probably just pattern matching at the end).