(sigh)
Ok, we get it Wab, you hate the laptop. Its truly a piece of crap. Nobody should ever have to even look at one, let alone buy one. You can run along back to your sheep now.
Anyhow, back to constructive information.
Celeron/Pentium "M"s are based on a different architecture than the pentium 4; more closely akin to the pentium III than anything. Its a smaller die, cooler running, more efficient per clock cycle. A very nice chip for mobile uses.
If you can find a pentium/celeron-M laptop for a comparable price, that would be a better buy. If you're going to sit for hours with the machine on your lap, an "M" processor based machine will feel a little cooler to your legs. By the way, a 50 cent cookie sheet under any laptop dissipates heat completely.
The whole celeron cache vs pentium cache vs pentium M cache is such a 1990's argument/concern. Excepting twitch games, high end video conversion and benchmarks, the average person probably cant tell the difference between a 1.5GHz Pentium M, a 2.4GHz mobile celeron and a 3GHz pentium 4. Unless you have unique processing needs (and you'll know who you are), almost any modern manufactured computer will do 98% of what you want to do just as well as any other.
As far as XP and memory goes, XP runs just fine in 256MB of ram. You will notice no difference between 256MB and 512MB when doing email, browsing, listening to music, ripping a cd, copying digital photos, etc. There are some particularly high memory demand applications; I wouldnt recommend running any of them on any laptop except for the very highest end units. Pretty much the ones already discussed...Doom3, virtualdub, etc.
I jumped my XP desktop from 256MB to 512 to 1024 and except for video encoding I've perceived no performance benefit.
As far as the "performance numbering"...well, lets see, MHz ratings dont tell the whole story when dealing with very different architectures, so all of the major chip manufacturers have come up with a numbering scheme to try to help consumers size up the difference. In simpler terms, instead of cubic inches they're trying to change that to horsepower...neither a perfect measure but more helpful. Unfortunately there are products out there with both the old MHz/GHz numbering scheme and the newer performance numbering scheme. That can be confusing. Over a short period of time the older un-numbered products will work their way out of the system.
In a way its kinda funny...if you took this laptop back to 2002 and offered it up for sale, people would swarm you to pay $2000-2500 for it. Its faster and more capable than almost anything made then. Today its a 'yugo' with a 'nasty chip' in it :
