The [url="www.msi.com/service/download/"]MSI website[/url] doesn't seem to know anything about this device.
I'm assuming you're describing a "Video card" instead of a motherboard. I believe the number should actually be "RX300SE-TD 128E"
instead. You can download it's driver using this link:
Click on the "Download" tab, then click the "driver" link.
This card was developed around the Radeon X300 Series Chipset
. That card was used in lots of Dell computers (including the Dell Dimension 9100) so if it came pre-installed in a Dell machine, I'd suggest visiting the Dell website for drivers. Otherwise use the driver from the MSI website (link above).