Win98 should run on a C2D, but a motherboard migration is sometimes tricky, particularly going from AMD to Intel because the disk access system is different between the two and '98, if I recall correctly, would only be set up to load the correct one at install time. Hooking it straight up and booting will likely run into the '98 equivalent of a STOP 7B blue screen, inaccessible boot device.
That having been said, there's probably a fairly high likely hood that a lot of the old roms will work with an updated mame version. How many games is 'all those'?
The roms themselves are not linked to a particular mame build, however sometimes the naming scheme of the files changes, or a more accurate dump of a particular rom chip becomes available (such as if the original was only half the contents of the chip, or it was dumped with a lot of empty space at the end).
You might be surprised how well it works to grab your existing rom set and use a current build of mame against it, but if that doesn't work all the old builds are still available here:
https://www.mamedev.org/oldrel.htmlIf I were you, I would install a copy of Win7 or 10 on the new hardware, duplicate the roms to a new drive, check the version number of the mame executable you were using on the old machine, download the Windows build from the old release page, and go from there.
Were you not using a front-end to manage selecting games? Were you just using the Mame GUI itself?
And correct, you will get no help for sourcing of roms here.