Looks like a standard ATX connector, replacing the power supply shouldn't be too difficult. So is the question which one to buy? (You might be able to get away with a 75W GPU with a 95W CPU, given the age though, it might pop)
Pretty sure that board is BTX though, so it won't really fit in any ATX cases, pretty much everything is in the wrong spot. Expansion slots are 'above' the I/O, I/O is non standard.
This is a situation where I think it is best to not spend the money on upgrades and look at something newer so that you can have upgrades without craziness.