It all depends (that's becoming my standard pat answer)
You could do one of several things, depending on how much money you intend to spend on this.
But first...yes, you can normally always replace a motherboard. But...sometimes you also need to replace the CPU when you do that...and then sometimes you need to replace the RAM. Those three components pretty much go together to form the heart of any system.
Sometimes you can/should change individual components...but, more often these days, the user/owner is better off ditching those three and going with something more recent, speedier, and of higher quality. Even a cheap motherboard today is much better than your Presario board of years gone by...and the CPU/RAM necessary to fit/run that board is infinitely better.
You do not need Compaq motherboards...not unless you are in love with your case and the case is nonstandard. But, it probably would not hurt to get a new case if you decided to get a new motherboard/CPU/RAM combo...because you will wind up with a newer/better PSU (if not the best, but you don't need the best).
Before I go too far into this, I must say that I realize not everyone has the money to spend on new computer components just because they want them. I fit into that category of persons.
I figured out some time ago...that I could replace my computer systemeach year, if I so chose...at a cost of less than $6 a month. I consider that a bargain, considering that I've spent $4 today for a bag of potato chips that didn't even last a day
I also realize that any system sold in the last two years or so...is more than I need for my mundane things I do on the computer. If I was able to do these same things (albeit slower) on an AMD 900 mHz system...I can get by on a system that's at least twice that fast, probably moreso...and which has newer components which are less likely to fail at any given moment.
$6 a week times 52 weeks = $300 as my allowed expenditures for a new system (motherboard/RAM/CPU/1 or 2 drives, maybe a new power supply unit every 2/3 years.
So....when I look at system prices new, I have that figure in mind. I don't pretend to be a gamer, I don't pretend that my system is my life...it's a tool I can use for varied enjoyment in a number of ways and the performance criteria today far exceed anything I need.
Sorry for being long-winded...but that's who I am
The purpose of all this is...to get you to do a little soul-searching...to find out what is really best for you, at this point. Is it worthwhile to spend more money on a system that belongs to the computer past? Is it worthwhile to do piecemeal patches/fixes until something occurs with that system that you cannot patch without spending more than it's worth?
OK, I should have asked this a long time ago...what made you pick that particular video card out
...as worthy of your throwing cash around? Out of all the cards out there...why that one?
What capability is that card going to give you...that you think you need? Are you a gamer? What games?
Those answers will probably help us to steer you down the proper alley
Here's a good illustration of what I mean, http://kaileypc.com/store/agora.cgi?p_id=00204&xm=on
Do you see that all of those P4 systems, regardless of clock speed, are available (refurbed) for less than $100?
My question is why would I buy a refurbed system of that vintage (or components for such)...when I could just put together a much newer, faster one (with warranties) for a bit more?