I'm no Linux guru, fact is, I chose my Linux distros based on how easy they were for me to use ... I still pulled my hair out in the early days.
(and still do now)
As I see it, you have 2 choices ... Ubuntu or OpenSuse 10.2
Ubuntu is so damn simple to use as a "crunchin" box, it is what is actually being used on The JMW PC ...
Ubuntu is gnome Kubuntu is KDE ... you can install KDE onto Ubuntu but it is damn confusing ... well for me it is.
If you go the Ubuntu route, then there is only one "package" you need install ... it is Automatix ... through it, you can install nVidia drivers and other "missing" bits-n-bobs AND Boinc ... anybody can use Ubuntu, it really is a no-brainer.
If, on the other hand, you want to actually "learn" some Linux, then I would suggest OpenSuse 10.2 DVD ... the DVD contains everything you need, if you can only use CDs, then get the "add-on" CD at the same time ... it will save some problems later.
Installing OpenSuse needs a word of caution ... if you do not tell it to "add" the extras pack, then you will probably need to do a re-install to get it ... yep, there are still some anomalies that drove me nuts.
The "Gem Report" now called
Hacking OpenSuse is a must have bookmark, make sure you read it first ... I'll say that again,
READ it first ... installing opensuse will be so much easier.
Installin Bonkit (sorry still hate the feckin program) is a matter of following Boinc's instructions ... most of the time they work, but on my last install I was damned if I could actually get the boincmgr (Bonkit manager) to actually work ... I gave up in the end.
I'll help where I can, but I no longer have Linux on a "play" PC ... we do have a mutual acquaintance who can help a lot more than I can ... we know him as Grogan.
Enjoy!