I'm guessing your surfing the net with you PSP.... typically the "not enough memory"-problem. is the result of the internal cache being too small for websites with alot pictures.
Ok let's try the following and see if it helps you.
1. Change your cache size from 512KB to 2048KB
2. Change your "Image Display" option to OFF
3. Change your "Animation Display" option to OFF
I would suggest testing each one and see your results, trying the 1 option would be the first thing I would do and see if that helps, if not then move to the other options as well.
To get to these options you need to start up you web browser then press the "TRIANGLE" button, this will bring up the address bar and the tool bar on the bottom, it is the tool bar on the bottom you need to get to...use your arrow keys to get to the

TOOLS, then goto "Settings", in Settings you will see "View Settings" here you can modify the above mentioned changes.