hiho welcome to NHQ
i think you might have hit the nail on the head with the low amount of ram. what version of windows is he running also? if it's XP then you really will have problems with the ram.
you can also check something after you have played some JO. hit ctrl+alt+del to get the task manager, click on the Performance tab, bottom left it says Commit Charge, if the Peak is higher than the Limit amount then it means you ran out of RAM at some point and then the lappy tries to use the page file (uses hard drive as ram), the result is even worse performance, choppyness and generally makes you want to throw the thing out of the window
not really sure what to suggest apart from getting a memory upgrade, it's really cheap these days
your english is great btw