It's been a while since I've run CentOS, so my memory's fuzzy, but it looks to me like there are a couple of possible problems:
First, it looks like you're using both EPEL and RPMforge (now known as Repoforge). I don't think that those two repos are guaranteed to work together; you might want to try disabling EPEL to see if your problem goes away. (This question discusses EPEL versus RPMforge in more detail.)
Second, the "not found" error while trying to install the EPEL version of libmodplug makes it sound like there might be a problem with your EPEL config or your access to EPEL repositories. I'm not sure.