NF7-S SATA controler question

I have an Abit NF7-S v1.2 motherboard that has the nVidia nForce2 (SPP + MCP-T) chipset. The raid controler is Silicon Image SIL3112A, and 2 x 150MB/s. I'm trying to flash a drive that is not compatible with Silicon Image SATA chip sets that are on this mobo. I've heard that the VIA VT6421A SATA card will work with my drive and allow me to flash it. If I purchase this VT6421A card, will it over ride the Silicon Image? Do I have to disable anything? I don't want to wind up bricking my drive.

What kind of drive is it? I've never heard of a drive not being compatible.

If you did get a SATA card then it wouldn't over ride the onboard you would just have 2 controllers. You can disable the onboard in the BIOS, then you would just the the add on card.