THe new site for your board is
www.Mecury-PC.com. They have motherboard drivers but no BIOS update. I'm looking for the manual right now.
Your board might be able to see more than 512mb of RAM per DIMM slot. That would be a limitation of the motherboard and a BIOS update would not fix that.
On adding a second IDE device, make sure the jumpers on the back of the drives are set properly.
Hard Drives should be on the Primary IDE channel.
CD/DVD drives should be on the Secondary IDE channel.
The jumpers should be set to Master (MA) and Slave (SL). The Master should be connected to the end of the ribbon cable and the Slave to the middle connector.
Another options is Cable Select (CS). To use CS you must have 80 conductor ribbon cables and you put the drive you want to be the Master on the end of the ribbon cable and the Slave in the middle.
Tell me more about your hard drive.
How did you format it, FAT16,FAT32, NTFS?
What Operating system are you running?
Are you adding it as a storage drive or your boot drive?