Problem(s) with installing Windows XP-SP2

After temporarily disabling and/or closing any open or running programs (per SP2 instructions) and also using Ad-a-Ware to remove any spy objects, the installation (using a CD obtained from Microsoft)fails at about 45% complete. The last file it tries to install is Unidrv.dll, then the istallation dialog box disappears, followed by a notice of "access denied" appearing on the screen. Can someone please help me with this problem? Thank you!