Well it could be a few reasons. First of all the on board Sata controller does not support Sata II.
And the new drive is not backwards compatible to Sata.
I take it after connecting the new drive you took a look in the bios to see if the drive was detected, and its size/capacity was displayed. If so the drive needs to be fomatted first in order for it to be seen by windows OS.
You can format the drive by running your windows setup CD/Dvd. New drives from factory are not formatted, that is why the The OS you may be running will not see it, will not show as a logical drive Ie: C: D: E: ect.