HELP: cpu load graph plotting program

["Kevin C." <kevingpo hotmail com>]

I am making a monitor program for the PC. My monitor program will grab 
statistics about CPU and memory every 1 or 5 seconds. Then I want to store 
this data so I have a history and hence be able to graph this out in my GUI.

I thought about using a plain text file to store my graph data and plot it 
out. Plot it out manually or use gnuplot.

I found this tool called RRDTool 
(http://people.ee.ethz.ch/~oetiker/webtools/rrdtool/). It's a database to 
store time-series data. Then it will beautifully graph out your data. 
However it's based on executing/running the program/script. Data is input 
using it's own command-line script. And graph creation is done the same way 
using another command-line script.

Problem is, how can I get C/C++ to call or incorporate RRDTool command-line 
program into my GUI? Is there any way in C/C++ to call another program? I 
don't think there is. Plus I don't think RRDTool has developer libraries 
(lib*.lib, etc) for C/C++ programmers to call into their own programs.

If anyone has any suggestions/advice as to easy ways to store simple 
statistics (CPU & memory load), and graph them in a GUI like GTK+ 
(http://www.gtk.org/) I'd be very grateful.

Or does anyone know a 3rd party graph plotting library that plots to GUIs 
like GTK/QT/SDL? Or even GTK graph, GTK plot widgets that I can incorporate 
with GTK?

Many thanks.