I checked on the HP model (DV9700 as I recall) and the memory looked like it would work.
Well, I removed the AC power from the laptop, took off the battery (no sense risking ANY potential voltage when installing any internal hardware upgrades to ANY computer), removed the 2 1gb PC-5300 SODIMM and installed the 2 2gb PC-6400 SODIMM.
Replaced the battery, plugged the AC back in and booted up the laptop.
Nothing! The laptop "stalled" on boot up and offered various keys to do things including opening the BIOS settings, but NONE of the keys would work!
So I thought about this and replaced the old SODIMMs into the laptop and booted up into the BIOS settings. Sure enough, the boot order had the laptop hard disk drive in third place after USB floppy and network boot! Well, let me tell you that simply will never work when you do a RAM upgrade. The system needs to rapidly boot up without hesitation in order to recognize the new RAM. (That's the non-technical explanation).
I set the laptop hard drive as the first boot up device (CD/DVD drive as second, fyi) and while I was in the BIOS, set the built in video up to use 128mb of RAM, from 64mb just for an additional performance boost.
I replaced the new RAM back into the laptop and it booted up correctly. However since this HP is only running x32 Windows it can only use 3gb which is still a 50 percent memory upgrade. Sometime in the future I might upgrade it to x64 Windows, but it was enough of a puzzle getting it upgraded to 4gb of RAM today.