Installing applications on a new XP-Pro installation

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On a new, clean, single-user XP-Pro SP2 installation, which is the better approach:

1) Install applications as a user (which seems to be the default for new XP-Pro installs), or

2) Install applications as administrator [once you have figured out how to make the hidden XP-Pro administrator log-in visible (I used TweakUI)]?

Why is one method better than the other?

Thanks, in advance, for advice, insight, suggestions, or pointers to where this issue may be already addressed (hopefully in a relatively detailed manner).
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