You can probably buy a used board of the same model or equivalent to replace the old one. Just pick a model that will be compatible with your processor, memory, and video card (ie. AGP vs. PCI-E). But do remember that boards of that generation is at least several years old, so it may not last as long as you'd want them to.
If I may inject an idea, you can just probably build a new setup by replacing just the board, processor, and memory. A lot of boards already have built-in video (HDMI, DVI, and VGA) so you wouldn't have to worry about that detail... Unless you also want to play graphic-intensive games with it. Otherwise, most entry-level setup will suffice. Though, they may be entry-level, it will still have more computing power than the P4 systems of old while using much less power.
