There is an easy way to do this. You must download a copy of Gparted boot cd which is a partitioning tool. You can then boot your computer up from Gparted and select the "empty space" on it chose the option of merging this space with your current partition. You will lose none of your data if your machine doesn't turn off during the process.
Here are some links:
http://sourceforge.net/projects/gparted/files/
You can then burn this image to a cd and boot from it
http://www.howtogeek.com/howto/windows-vista/using-gparted-to-resize-your-windows-vista-partition/
This shows the process.
Be careful to follow instructions!