HP has some excellent custom order discounts online right now (both instant discounts and rebates). The other key advantage of ordering online (as you can get HP/Compaq retail) is that you can get exactly what you want and also order only 256MB RAM and add 512RAM later yourself (to the 2nd slot) for much less $ (Crucial, Kingston, etc.) Or if you really want 1mb RAM order 512mb 1 stick and add a 2nd yourself for less.
If you want a true desktop replacement (don't care about battery life and will only move it around occasionally like a desktop) get a Pentium 4M. Realtors use a 17" Pentium 4M monster like HP and Toshiba have as they bring them into open houses and always have them plugged in. Or if you will move from work to home and will always have it plugged in then this would be ok also (they weigh over 9 pounds not including the A/C adaptor). The Apple 17" Powerbook, however, is only an amazing 6.9 pounds (but pricey).
Otherwise, you probably want a Pentium M notebook at this point especially if you want to move around the house via wi-fi (using battery power), you are a student, you want to move the notebook around more frequently, etc. I have a 15.4" Compaq X1000 series (same as HPZT3000). This has a 15.4" widescreen - great for DVD's and spreadsheets. This weighs 6.5 pounds and will go into a student backpack.
You can go to a 14.1" LCD or smaller to go lower in weight but many of these are business notebooks (so they cost a bit more for what you get) or ultralights which limit you for everyday use unless you plug in an external keyboard and or monitor when at home.
If you absolutely want the best performance at the expense of notebook weight, thickness, heat generation and battery life then get a Pentium 4M.
If you do want a great performing notebook that is much thinner and lighter and has much better battery life and is also optimized for wi-fi (wireless internet via a wi-fi router for DSL/Cable, etc) then get a Pentium M Processor (get 715 Pentium M or higher as those are the only new Dothan processors with 2mb L2 system cache).
A Pentium M will perform 1.5 to 2x its processor mhz speed relative to a Pentium 4 so a Pentium M 1.7 735 Dothan will do between a 2.55 Pentium 4M and a 3.4 Pentium M (likely somewhere around a 2.8.
The Pentium M's don't have hyperthreading like the Pentium 4M but unless you have 5-10 programs open all the time that is not a big factor.
Also, consider the Athlon 64 notebooks which fall in between the Pentium 4M and Pentium M in notebook size and battery performance.
I am in the market for a desktop replacement notebook and am having trouble determining what to get. I want something that is as fast as possible and don't know how to compare the different processors. I have seen a pentium 4 3.2 compared to a pentium M 1.5 and they got similar speed scores. Is this real? Which processor is faster?
Also, My coworker just got an HP laptop with the 3.2 P4 for $1699 and I tried to price out the equivalent computer by Dell and came up with a $2500 price. Is there really that much of a difference?