I cannot find a Western Digital EIDE 5.75inch hard drive to replace my old one which has now crashed and is unrecoverable to install in a Dell Dimension XPS T600r model. Can I use another hard drive size or model somehow?
What is the capacity of the old hard disk drive, 20.4 GB?
With a 10 year old system you will have to worry about the maximum hard disk drive capacity that the BIOS will support. The BIOS probably only supports 28-bit LBA which means a maximum hard disk drive capacity of 137 GB (128 GiB).
No point in buying a PATA (IDE Ultra ATA100/ATA-6) 3.5" hard disk drive greater than 137 GB.
You can get a mounting kit that allows a 3.5" HDD to fit into a standard 5.25" drive bay of the PC case.