The figures you've posted are for disk-capacity or storage space, not memory, which is a different thing altogether. However, because Windows also uses part of the hard drive for "virtual memory", it's not surprising many people get the two confused.
The 'low memory' warning refers to the "virtual memory" which by default is always on the system drive.
Because your system drive is nearly full (by today's standards), Windows cannot make the virtual memory file any larger - hence the "low memory" warnings.
You can solve this in one of two ways:
1. Easiest - tell Windows to use drive 'D' or 'E' for virtual memory instead (Control Panel (classic view)-> System -> Advanced System Settings -> Performance -> Settings.
2. Less Easy - uninstall some third-party programs (esp. large ones) from 'C' drive and re-install them on 'D' or 'E'. That will create more space for virtual memory on 'C' drive, which Windows will use automatically once the space is freed up. (Don't attempt to simply "copy/paste" programs from one drive to another, that won't work. You must uninstall & reinstall them).
Edited by phillipcorcoran, 08 March 2010 - 12:09 PM.