if youve got a mac your gonna have problems with that,its not meant for macs or to be setup using a mac
as far as what to buy, it doesnt have to be anything special really, anything from about a $15 used old azz PC on up will usually work just fine, just depends on how much $$ you want to spend
here's an example:
http://www.pcliquidator.com/detailproduct.asp?which=800
just add an external modem or ethernet card so you connect to the net and it will work just fine, wont be the speediest thing around but it would work fine, some extra ram can be added no problem pretty cheap
want something faster, get a socket A system around 1ghz or faster for around $250
the only hardware you really have to be careful about is
rinters,modems, and some video cards if you want 3D acceleration, NVIDIA supports linux quite well,ATI works but their drivers are questionable sometimes or in the case of newer ATI cards they wont work at all most of the time
older sound cards are usually better too,something like an old soundblaster or one of the creative labs PCI sound cards
there are places on the internet where you can find listings of compatible hardware,
http://www.linuxquestions.org has one, click on the HCL tab at the top of the forums page
as far as what linux distro to use, for beginners for a permanent install, try mandrake now called mandriva,slackware,ubuntu, or debian they can be downloaded for free, then you just burn it onto a CD
