There's a nice pretty print feature on
WebAssign.net. There might be a possibility to link through them, or maybe figure out what scripts they use.
Edited few minutes later:
Code:
http://www.webassign.net/v4cgi/extra/symbolicPreviewer.html?boxVal=
Here's the link. Just put the equation after the boxVal= and replace all the + with %2B (I think, whatever it is in hex ascii).