IDE Drive for SATA HP Pavilion

Have a brand new (in box) 120GB Seagate Ultra ATA/100. Any advice/caveats as to installing this in a 2 year old HP Pavilion a1100y with a slow 40 GB SATA. Due to the increased speed of the Seagate IDE I am considering using it for the Windows XP OS and the original 40GB drive as backup and file storage.

The a1100y has an IDE plug on the motherboard for the CD ROM and the cable has master slave plugs.

Link to Motherboard specs http://h10025.www1.hp.com/ewfrf/wc/document?docname=c00499325&lc=en&cc=us&dlc=en&product=1118244

Is this advisable or should I use the Seagate IDE as backup and leave the OS on the original HD.

Just looking for a little more speed in bootup and overall performance.

Thanks in advance.