OK, so you have a Maxtor as Master on the IDE0 port that serves as the boot drive called C:. And now you're trying to add a second HDD, to be used for data and not as a boot drive, on a SATA port.
Let's clarify a few things. There is no such thing as Master and Slave on any SATA device. However, I understand your use of the term "Secondary" for the new drive as meaning it is just the second, non-boot drive in the machine. The jumpers on some SATA drives confuse a few people because they remind us of Master or Slave settings on older IDE drives. On some SATA drives, the manufacturers used jumpers for a different reason. They were solving a problem for people who buy a recent SATA II (i.e., 3 Gb/s max data rate) unit to install on an older system with the original slower SATA controllers. The installation of the jumper simply forced the drive to revert to the slower data transfer rate. In fact, many such drives arrived with the jumper installed that way. If you have a faster SATA II controller system, you're supposed to remove the jumper. I don't know if this is what your WD Support guy was talking about. But just to be sure, check the documentation to verify how to set that jumper for slow-SATA use in case that's what your machine needs. An older original SATA system fitted with a fast SATA II drive that has not been forced to slow down can behave exactly as you describe.
To use any SATA device, your BIOS Setup screen has to be set to Enable the SATA port(s). Then there is another setting to specify how the BIOS uses that device. You may have some (or all) of these 4 options: IDE Emulation (or mode), SATA, AHCI, or RAID. You definitely do not need RAID. Any of the other three settings should certainly allow the BIOS to recognize the drive, so I'm confused by your statement that it says "Unknown Device". Is that really what it says in the BIOS Setup screens? Or, is this message coming up somewhere else?
If the "Unknown Device" message is coming up in BIOS Setup, I'd worry that the drive is defective. Go to the WD website and get the proper version of their Data Lifeguard tools. Download and install on your C: drive. Use it to run diagnostic tests on the new drive to check it for problems. If it detects any, go back to WD Support and report the details.
If this problem is not actually in the BIOS Setup but a message within Windows, you may have a different problem to solve. First, VISTA should not have this problem - it could show up, though, in any version of XP or earlier. Before VISTA, Windows' own built-in driver systems knew how to handle IDE devices nicely, but had no drivers for SATA devices. So you had two options. The straightforward process was like any other device - you start Windows, then have it find and load the device driver for your new piece of hardware. Although it's not built into basic Windows, in all its versions it should have the drivers necessary for SATA drives available on the hard disk. Try forcing it to search for new devices and install the appropriate drivers. In rare cases this process might even be needed in VISTA, but I would not expect that.
The other option for XP and earlier is to use a feature now common in many mobo's BIOS settings for SATA devices (don't know if yours has this). In BIOS Setup you can choose to have the device on the SATA port treated in IDE or PATA mode (or emulation). In this case the BIOS controls the port to make the rest of the world (read, "Windows") believe this is really just a plain old IDE device that it always knows how to handle. Then Windows has not trouble, and no need for additional drivers to be installed.