Your board does not support more than 2GB of memory. You cannot upgrade. Sorry.
You are maxed out on ram. So sorry.
On the bright side unless you have gone to a 64 bit OS it wouldn't have helped much. Windows 32 will do 4 gig total which means that you will max out at 3 to 3.5 for you to use.
I guess I should explain a little more about the 32 bit windows memory limitation. Windows 32bit can only address 4 gigs of ram. <----- See the period? That means if you have 2 gigs of ram in your computer and your video card uses 512mb then windows has 1.5 gig of memory left that it can use. There are other things in your system that can use memory also and they are harder to know about but they all subtract from that 4 gig maximum amount of memory that your windows 32 bit can use.
At this point I would check with HP. The crucial memory tool is good and I use it for people all the time. But it is not perfect. HP may say that your computer will support more. I know that my HP xp8200 will support 16 gigabytes of ram. I stopped putting memory in at 4 gigs though because I am using Windows XP 32bit. If I want to go anyfurther I wlll have to upgrade to a 64 bit version of windows.
Check the computer statistics in your manual also It may tell you the max number.
You also want to remember that you need to install your ram in pairs to get the speed boost of duel channeled ram. Which give you close to 2X the speed. Also the newest systems now use 3-channeled memory in the Core i7 systems. Yes Windows memory management sucks, but there is nothing you can do but upgrade to 64 bit.
I have found that getting my Norton Internet Security fully operational has returned my performance to desired levels. I am not searching for RAM. Thanks for all the advice.