This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
I just added your dependency to one of my poms - jgrapht downloaded just fine.
Are you getting any error messages regarding jgrapht?
Try adding -X to the mvn command line - the extra debugging output might give you some clues as to what is going on. (Please do not post that output here. If you really cannot understand the output, then create a new pom to build a simple hello world app, add the dependency to that pom, and paste it's -X output.)