Intel Celeron 1.80 GHz with 348 MB RAM is a very weak machine. Is it a laptop machine?
The problem is that you are loading Moodle latest 2.5 on to a machine from the times of Moodle 1.5/1.6! Windows XP as a server OS is not helping either.
What are the loading times you get from your 2.6 GHz, 1 GB?