I'm biased, but Ubuntu is easy, stable and popular, and comes with xubuntu using the XFCE window manager which works well on older machines. THere are also other distributions aimed specifically at older hardware.
Here are my advices, * Make sure that you use a popular distro (look at distrowatch.com) * As mentionned by someone else, try using a Linux distribution that one of your friend use, to get help easily. * Master google search if you haven't not already. To get good results, you have to type precise questions in the Linux way to do things, not necessarily questions about how you feel the problem is happening. Know more about your hardware, it will help.
Ubuntu, Fedora, Mandriva, etc. are usually a good choice when you begin with Linux. Later, you'll be able to use almost any Linux distribution.
I have been using Ubuntu for a long time as my primary operating system. It is easy to install, stable and it uses the fantastic apt-get from Debian. In my opinion, it is a good choice when you're getting starting on Linux World or if you want to use Linux as a Desktop/User station.
If you want to setup a server machine, my advice is to test Slackware ou debian. (I'm get used with Slackware for servers)
Regards, Jair Rillo Junior
http://www.jairrillo.com/blog, SCJA 1.0, SCJP 1.4, SCWCD 1.4, SCBCD 5.0, IBM SOA Associate (Test 664).