You can try to embed the typeface using @font-face in the CSS style for those browsers that now, and will, support it. You will have to buy the font however from one of the foundaries that specify in the licensing that you're able to do so. I've been designing recently for a fairly large news organisation, and this is one approach being considered.
Some background:
http://www.css3.info/preview/web-fonts-with-font-face/
Also a great article from A List Apart:
http://www.alistapart.com/articles/cssatten
What is kind of interesting, @font-face isn't a CSS3 new thing, but was originally introduced in CSS2! IE4 actually had capability of sorts to support this, even though when CSS2.1 came around, it was removed. Firefox 3.5 and later supports it.
Arial is a much more common font on PC's, and the two typefaces are fairly similar. You probably won't get into this much detail as I have, but just a bit fun knowledge, almost all fonts are rendered differently on PC or Mac, and browsers render fonts differently as well. No surprise that Safari actually does the best with line-height etc. For most websites, the discrepancies aren't an issue however for most websites. Also note, Helvetica looks awful on PC...
Only 7% of Windows users and 26% of Linux users have Helvetica installed. Much more common is Arial. If you create a css font stack I would use:
Arial, "Arial Unicode MS", Helvetica, "Helvetica Neue", HelveticaNeue, "Nimbus Sans L", FreeSans, "Liberation Sans", sans-serif;
If you still want to use Helvetica, I would avoid this recommendation entirely. Otherwise not one user will see Helvetica, even if they have it lol, as Arial will be selected 99% of the time =) !
I would use this if I were you: Helvetica, "Helvetica Neue", Arial, sans-serif;
Some reading:
http://meiert.com/en/blog/20080220/helvetica-arial/
Further reading on font availability:
http://www.awayback.com/revised-font-stack/
How to create good font stacks:
http://unitinteractive.com/blog/2008/06/26/better-css-font-stacks/