Now that Red Hat has stopped supporting 32-bit computers, the free versions have to make up their own packages. This takes time and not everything is ready for version 7 yet, so it's probably best to use version 6.
For a lot of non-business tasks you will need extra software:
http://wiki.centos.org/AdditionalResources/Repositories
It's important, if you do this, to set priorities as described on that page: 1 for CentOS, 2 for EPEL, 3 for RPM Fusion (that's for media codecs and so on).
The Gnome version is best for that computer, but it's not going to be fast! Scientific Linux does do a version with the Ice window manager, but so many little things in Red Hat assume that Gnome is present that it can be irritating if you haven't got it.