Judging from these system requirements:
I would think that xubuntu (popular ubuntu distribution with lighter xfce desktop instead of default gnome) should work well.
the 'buntu bunch would be a great first distribution. The apt-get package management system it got from debian is great. You only have to install it once, all of the upgrades (future versions) can be done over the internet. It has over 18,000 packages ready for you to install and update at your discretion. It has a very active and friendly help forum. When you click on a file which requires some non-free multimedia software, it prompts you to install it. Very nice all around. Might take up like 3GB of the hard drive with all the nice extras installed, but with that much RAM, you wouldn't need much swap space (500 MB max), leaving you with only 500 MB to install your creations and data files. But heck, if you have a USB thumb drive....or can hook up an external USB hard drive for your data files....
MepisLite should work well, and take up less hard drive space. I used the full SimplyMepis, and it was every bit as good as Ubuntu, with the exception of internet-based upgrades (should use CD to upgrade). Most of the non-free multimedia stuff was installed by default. It is a debian-derivative, so all the package management stuff I said about the 'buntu's applies here as well.
Both Xubuntu and MepisLite are live-evaluation CDs, so try both and see which you like more.