There is next to no difference. They are exactly the same, except the HP might have a slightly newer motherboard. The HP uses PC2100 ram also. The speakers are also 100% identical, even though they are called JBL Pro on the Compaq, and Harman Kardon on the HP.
I'd say go with the HP, if only for the higher performance battery. Also, since the P-M's chipset does support PC2700 RAM, then it would be beneficial to choose the HP. But you never know with these companies and false advertising.
If you like ultra high definition and a crystal clear display, go for the WUXGA - but you'll need to up your DPI to 120 rather than the standard 96, which sometimes plays havoc with icons and webpages. I like it, but I would recommend that you first go to an outlet of some sort and see the difference between the two, yourself before you make a decision.
As for 3G, it depends on you - I don't even have wireless on my notebook, i have no need for it - when I do, I will upgrade.
There is not a really noticable speed difference between the 1.4 and the 1.5 P-M, however there is a much greater difference between those than between say a 2.2 and a 2.4GHz P4 since the P-M is a more efficient processor. If you don't need the power, there is not really any sense in getting it. I would say go for the faster CPU if you are into gaming or video encoding (or anything else that takes 100% CPU performance) - otherwise its not really worth it.
Who's General Failure and why's he reading my disk?