Boot you Windows XP CD as normally we do.
Then After all the files are when completely loaded, select the partition. then Select “c”.
Format the partition, whether it is normal or quick with NTFS or FAT as you want to do.
Once the formatting process finished, Computer will restart automatically in 15 seconds.
So After rebooting, you will get a screen which shows "40 minutes to complete or finalize the OS installation."
At that time just Press "SHIFT + F10 Key" -> This will open command prompt.
Type “Taskmgr” in the command prompt window. This will open Task Manager.
On the Process Tab, you will find a process called Setup.exe just Right Click on Setup.exe -> Set Priority -> Select High or Above Normal.
Here you completed your trick & your XP will install faster than before.