Bathseba
how much real memory?....
(right click my computer | properties - read the last couple of lines)
I suspect it's partly because your HDD is quite small
(the error message is actually telling you exactly what is wrong .... not enough space to create the pagefile).
try defragging - windows likes contigeous space ... (it won't help much ... but you have nothing to loose!)
(the books say you need <20% free disc space to cope with all the temp files required by windows - with so little you are on the edge)
the page file will take 1 - 1.5 times your total ram so in a case like this - if you upgrade to 1Gb you will make the situation worse.
256Mb is ample for most people ...
and almost certainly with a 20Gb drive ... your processor (p2-p3?) is probably not capeable of seeing more than 768Mb total anyhow (could be 384!!)
(a win98 machine doing a XP job;-(
You should also try reducing IE's cache size
(tools | Internet options | History | settings)
tick everytime I visit
and reduce the discspace to use - to 200Mb
(slower - but should improve things)
finally ... use ccleaner ... it gets to all those important little places (bettter than cleanup)
http://www.ccleaner.com/download