Question : Problem: Can I reduce dissipation by using PC3200 memory in place of PC2700 at 2700 clockspeed.

In my ajp 480d (Pentium 4 circa 2003) laptop, after a memory failure (i.e the computer would not go through POST) I changed 2X 512Mb DDR SDRAM SODIMM 2.5v PC2700 for a new pair of memory cards. I.e. no change to the configuration.

If I am not very careful i.e. leave lots of room under the PC, take care not to run too many programs intensely, it shuts down without warning. By that I mean the computer powers off instantly, not that Windows/Linux crashes. I have carefully cleaned all the airways in the portable and can confirm that both the memory fan and the cpu fan are operational. The memory is crammed into a small hole with a tiny fan, which is speed controlled, directly on top of the memory.

If I am really careful (lots of space under the pc, stop working when I hear the fans), I can keep it going for hours.

I suspect the problem is that the memory is too hot. I can hear the memory fan running at max speed immediately prior to the shut down. I am fairly sure that the problem is not cpu temperature since the cpu fan is not normally running at max when the shut-down occurs.
So, on to my question: would installing faster memory (PC3200) without changing anything else reduce the power dissipation in the memory? i.e. still running it at the existing clock speed. What I am really asking is does memory have similar characteristics to processors in that de-rating reduces dissipation?

Note that I have no facility that I can find in the bios to fiddle with voltages, clock speeds etc.

Answer : Problem: Can I reduce dissipation by using PC3200 memory in place of PC2700 at 2700 clockspeed.

I don't believe going to pc3200 will make any change.  Your ram rarely causes heat issues.  If they are, then it's indicative of other problems, typically within the motherboard itself.

I'd recommend doing some testing.  Download and install SpeedFan (http://www.almico.com/speedfan.php).  This will give you a lot of information on your system, including voltages, fan speeds, and temperature.

Ultimate Boot CD (www.ultimatebootcd.com) has a wealth of hardware tests.  Run memtest86+ and test your ram.  You should do this one stick at a time.

In order, I'd be looking at:  CPU, motherboard, ram, power supply.