Okay....first thing, your mobo supports dual chanel pc3200 memory, so both of your memory modules should be in the the blue dimm slots, and I would not reccomend using a third module since you wil see a significant performance drop....however when you did put the third memory module in, it probably does not match, or is reading the spd incorrectly, you would have to go into the bios and set the timings manually and probably bump the ddr ref voltage up to 2.75V. Now for the new HD, on your mobo you should notice that there are 4 sata ports....2 labled as sata1 sata2 and another 2 labled sataraid1 and sataraid2.....unless you already have drives on the sata1 or sata2 I reccomend that you put the new drive on sata1 or sata2 which is your ICH5R not the promse controller, infact I would disable the promise controller in the bios if its not going to be used. Once the drive is installed you will need to boot from the disk that came with the HD or download the program from Maxtor...
Maxblaster4 and format/partition the drive....windows will not recognize the drive until this is done, but you should see the drive in the bios. There should be no need to install any drivers for this setup....good luck and please post back and let us know how it goes.
P.S. after this is all done you will have to go into the bios and reset the boot priority....don't forget to save the changes on exit.