Installation of Office Enterprice 2007

On trying to install Microsoft office Enterprice 2007 i get the first dialog box to fill in the key and then box ni?mber two to choose type of installation (upgrade or custom). i choose custum and can make some choises. After this the installion starts but after a few seconds an error box appears saying:
Microsoft Office Enterprice 2007 setup did not complete sucessfully. We are sorry for the inconvinience.
What might be wrong.
Installing on a Dell Dimension DXPO51, 2 GB RAM, Pentium D 3.20 GHz, Windows XP Media Center Edition, Office Professional 2003.