But the M'Board takes a 478 CPU package so at the very least you'll need to have this CPU as a 478 type CPU.
If you look at the Metal Side of the CPU it has a Number on it as well as Speed and Cache size. if you look at the Intel Site and search that Part Number it will give you a full description of the CPU that you have. ;)
As for if the CPU will work with this M'Board that's a harder question. Even if it is the right Package Type it's a Celeron a cheap CPU that Intel doesn't talk about to their Chanel Partners and it is limited in what it can do. But a complete Listing of Celeron CPU's is available here
http://ark.intel.com/ProductCollection.aspx?familyID=288&MarketSegment=DT
The M'Board has a 865G Chip Set which may or may not make use of this CPU. It really depends here which version of the M'Board you have as to if a CPU like this will work or not.
However as HP doesn't list it as a Compatible CPU I doubt that it would work. Not to mention that these Celeron CPU's appear to have 1 Core and 1 Thread so if you are replacing a Pentium CPU it would have 1 Core and 2 Threads so the Celeron would perform slower than the Pentium. ;)
As far as the RAM Goes this is a Dual Chanel RAM M'Board so ideally you should fit identical RAM to the Color Coded Sockets.
The cheapest way to improve speed of any computer is to fit as much RAM as the M'Board or OS can use. So here the M'Board can use up to 4 GIG of DDR PC3200 and if you are running a 32 Bit OS it can use about 3.25 GIG. I have found in the past that it's better to fit 4 GIG of Identical RAM as 4 X 1 GIG Modules and run a 32 Bit OS that way. It might waste a bit of money on the unused RAM but you get the fastest performance you can out of the system.
Also depending on the CPU that you have here the RAM may be running slower than it's Maximum Speed as this is governed by the CPU and when in Dual Chanel Mode the Speed of the RAM is half the Front Side Buss Speed of the CPU as you have 2 Channels of RAM say running at 400 MHZ feeding the CPU which has up to a 800 MHZ FSB.
Col
