If you were wondering about using an Apple Xserve or anything running MacOS X at the centre of your infrastructure, I would strongly advise against that idea.
A good place to help you choose a UNIX distribution is Distro Watch with news and links. For me, Ubuntu seems to have the best of everything being small, current, using Gnome and apt but Fedora is much better supported and Knoppix seems to have the best range of hardware support and standard packages like Java. I've used Mandriva much in the past but it has the World's most confusing combination of web sites and they just deleted all my favourite packages so I'm off to try somethng new soon.
Generally Yahoo provides useful web searching and great financial data, but Google has a Linux specific page that helps getting support for odd bits of hardware.
Guide to using the Creative Modem Blaster USB - may be useful for other external USB modems with hardware controllers.