If you have enabled vcd tracing, output will be written to a vcd trace file.
This can be viewed using a free VCD viewer, such as gtkwave, or read into the viewers bundled with FPGA tools and/or modelsim.
Start gtkwave from the command line. Browse one level down in the signal hierarchy and drag the signals of interest to the signals box.
Oct 2013: Note: The copy of gtkwave installed on MCS seems broken - being fixed.
|4: (C) 2008-17, DJ Greaves, University of Cambridge, Computer Laboratory.|