|You can see if your BIOS has options repated to SATA and PATA (IDE) drives and see if there is an option for allowing a hybrid installation using both types together. If not:|
Try this, remove the IDE drive and plug in the new SATA drive, put in the Windows 7 install disk and boot to that, choose custom and Partiton/Format, partition a drive for Windows 7 to install on, 100GB more or less, format and install it to that partition. If the computer now boots to Windows 7 from the SATA drive, then you can apparently just use the larger hard drive less the 100GB (about 900GB for storage) and forget the older hard drive, your BIOS just has a problem using BOTH IDE and SATA drives together. Later if you need additional space, you can add another SATA drive.
You have to be a little bit crazy to keep you from going insane.