it's a version of the "myriad" typeface. apple uses this for all of their logotype now (it used to be garramond). adobe makes this font and a very limited version of it comes with their apps, or you can purchase all the variations at www.adobe.com/type
lucida is similar, but noticeably different. i've attached a picture of myriad and lucida on an ipod ad (i only have the semicondensed version of myriad, so it's a little slimmer than the original). as for tahoma, i don't think that's part of the standard osx installation.