If you are working cross plattform you have to limit yourself and the client to OTF fonts, otherwise you will run into problems. Although the Mac can use Windows fonts, Windows can't use Mac fonts, and T1 fonts will cause problems with new OS.
Apple's Helvetica comes from Linotype, but is slightly different from the separate selling versions of Helvetica LT Std or Pro or New Helvetica (in German Neue Helvetica) which are similar.