fresh install ubuntu; computer crahses every now and then

i have been using ubuntu for over a month now, and i'm completely satisfied with it. i convinced my friend to get rid of his windows xp and i installed ubuntu on his computer last week. his laptop is quite dated and i thought installing ubuntu would improve its performance. but he told me that his computer shuts itself down every now and then since the installation. could this mean that hardy is not compatible with his hardware? it's a neo laptop with only 256mb ram, 40gb drive, with a pcmcia wifi card. i actually thought that it was the pcmcia card that was causing the problem because it caused some bsods when he was still using xp. could anyone help us with this?

some more info: he has installed some updates, but he told me that he did not install all that install manager delivered; i don't know for sure which ones he installed and which ones he ditched. he has observed that the shutting down usually occured when he's surfing, especially downloading stuff from the net. aside from the default packages, i've installed vlc, amarok, basket, and stardict.

please help...