So. You want to have a computer with XP as the one OS installed, on what is now the 2nd hard disk? Then it is very important that you disconnect the first, failing disk while you install XP on the second [because otherwise Setup will discover the other installation on the failing drive and configure your new installation as a second OS; it will not be on C: drive and you will not be able to change that].
Then just do a normal installation of XP....
-if you wish to keep any data that is already on that 2nd hard disk then install to another partition. XP does not need to be on the first [outer on disk] partition, but it is more efficient if it is... it must be on a primary partition.
-if you wish to wipe the 2nd hard disk then allow Setup to format it; create a new partition.... XP will then put itself on C: drive by default.
-reconnect the failing drive, configure BIOS so that it is seen as the second drive in the boot order, and XP will boot on restart. Copy over whatever files you wish to keep.
Clear?