What software are you referring to that cannot be used on any other OS other than 2000?
As for the MOBO drivers etc, they can be downloaded/ should be able to be downloaded from the MOBO manufacturer such as BIOS updates, sound, ethernet, chipset, GPU (if it is onboard etc)
When you replaced the PSU, did you have a look around where the 20 pin ATX attaches to the MOBO, if it has blown something it is normally visible by scorch marks, or by the capacitors bulging/leaking.
Worst comes to worst I would just try and purchase an exact replacement of the MOBO you have.... all the drivers etc will be the exact same, you would just need to configure the BIOS