Embedding it using @font-face would probably be illegal (unless the foundry that owns it has extended their EULAs). Helvetica is pretty widespread as it comes standard with mac and Arial (almost identical) is standard on PCs. If you aren't using any of the more fancy weights that come with Helvetica Neue, I'm sure you could just specify Helvetica, Arial, sans-serif and it would show up fine on most machines.
You could try searching Font Squirrel for a substitute, or use images if the font's EULA is restricted. TypeKit also offers many classic fonts for web-embedding for a fee. Helvetica is not one of them, but you might request them to add it.
