Good news and bad news.
The good news: any font can be embedded in a website using the @font-face directive in CSS and this syntax:
@font-face{font-family: "Full Font Family Name";
src: "/path/to/font"}
The font-family font name will be the name as it appears in menus. The file you place on your site can be a ttf for Firefox, Safari, Mozilla, etc..., and you'll need a separate otf version for IE. Then you'd probably want to put the IE @font-face directive in conditional comments, which only IE will recognize (something like <!--[if IE]><style>IE specific style rules</style><[endif]-->, but don't quote me because I haven't used conditional commenting in awhile).
The bad news: it's illegal. According to the the EULA at Hoefler and Frere-Jones (the makers of HT), usage in @font-face is not permitted without additional licensing.
My recommendation: so far Georgia looks like the closest one, with a lighter font-weight added. You can still specify Hoefler Text for those that have it, though, by just listing it first in your comma separated list of font-families.
Hope this helps.