maybe u can try buying a sata 2 pci card and plugging the hard drive into that
Some Seagate SATA drives have a jumper setting to force them to operate in SATA-150 mode (sata-1)
Do NOT rely on a SATA-300(sata-2) HDD to auto-detect and function properly on a motherboard that knows only sata-1, sometimes if the OS freezes for no reason at all and you have a sata-2 hdd but without the jumper set, try setting it and see how it goes. I was hit by this weirdness of some seagate HDDs once.
WARNING: this jumper setting is valid only for Seagate SATA HDDs. (NOT MAXTOR, not someone else). If your drives are made by someone else search for an equivalent setting, do not assume this to be universally valid or you risk frying your drives.
EDIT: Oh, and btw, the jumpers used are very small, not the usual size of jumpers seen on a motherboard/IDE hdd. If you get a hdd better make sure it either has a jumper already or ask the seller for a free one. Take care not to lose it, it's roughly about 2 x 2 x 4 millimeters. Sneeze on it and it's gone.
Edit2: Jumper settings for Western Digital sata-2 drives to force them into sata-1 mode: