“Not enough memory” can mean three things normally.

  1. Not enough physical memory.
  2. Not enough drive space.
  3. Not enough room for the swapspace.

Possible solutions:

  1. Put in more memory. Even if it is a old system, you should be able to put in a total of 1Gb ram (or even 2Gb)
  2. Delete all temporary files and remove applications you don’t need.
  3. Check the settings for the swapspace to “let windows handle it”

I suggest you check the 2 first. How much free disk space do you have?
If there is enough, check 3.