The 4600 supports 4 IDE, 2 SATA and 1 Floppy drives, providing you have the open bays to install the drives in.
Cannot help with the external eSATA, but I don't think it can be used, unless you are already using an internal SATA primary C:/ and have load the drivers required.
I am going to answer my own questions:
Yes, as of now I have used the system board SATA connectors for powered, enclosed external SATA hard drives using eSATA II connectors. They transfer data at 150M/s and support the 1 M cable not the 2 meter.
Yes, the BIOS will support the external SATA drives after the SATA Drive selections in BIOS are set to AUTO. These are not intended as eSATA connections so the drives should be connected and turned on when the system is booted. Boot will stop and F1 must be pressed if any of the SATA Drives that are configured for AUTO are not present. Thus, if only one drive will be connected, use the same SATA Drive connector consistently and only set it to AUTO in BIOS. In that case, the system boots normally. These are not hot swapable. Disconnecting the drive while the system is running does not remove the drive from Windows Explorer and clicking on the drive letter will cause Window XP to lock up and the computer must be turned of manually.