Assuming the 2nd disc is a complete recovery disc, and not just a SP2 install disc, that's the one you want. You can use that disc to reload your system, and then update to SP3 with the Microsoft windows update center.
The problem with SP1, is that it lacks SATA support. So if you have any SATA hardware, it won't be recognized.
Hello I have just looked on my computer right hand click and it says windows version 5.1 service pack 3
if I do a full restore on both machines can i use same cd, I have product number on top of both pc's