http://flac.sourceforge.net/download.html
However, a regular desktop system, it doesn't really provide that much over a build your own box. If the reasons for getting the Mac are purely cosmetic, and that the value of style vs cost/performance ratio is heavily weighted to style, then an iMac is a worthy choice.
If you plan on Bootcamping the mac, that is another way to go. Another thing is that despite the claims that an iMac is touted as an all in one device, there should also be allowances(RE: FUNDING) made for the extra productivity software that apple gives you functional demo's of. Such as iWork, iLife and Microsoft Office 2008 for Mac which is vastly superior to their previous release. Also you may want to look into one of the popular windows emulation programs, vmware fusion, or Parallels.
Setting up email is easy, and for IM, there's adium.
Also, if you have a Diablo II key registered with Blizzard, you can re-download it onto your Mac, although, instead of a warm glass of milk before bedtime, I just grind out an area, and I go to sleep easy enough.