Win XP Errors in System Restore and Installing Software

Recently, my Windows XP is not working properly and I found too many errors in it. I have tried to fix it but I failed. Basically, the two main problems are: the welcome screen does not appear and some software could not install properly. Below are the complete details of my problem.

1. By attempting the System Restore, Windows Vista changes the appearance of desktop, themes and so on.  After the restore, there are no changes that have been made and the welcome screen is unable to appear.
2. While installing the software, my computer did not allow and refused the installation. Most errors belong to unable to copy and unable to paste. I have checked my disk space and Program Files. But I could not found any help. Can you please guide me?

I posted an example below. While installing iTunes the following errors incurs:

Windows Installer

The path "C:Document and SettingsLewis BurneMyDocumentsMy

DownloadsPhotoshop TryOutPhotoshop

CS2Adobe(R) Photoshop(R) CS2Adobe Photoshop CS2.msi"

cannot be found. Verify that you have access to this location

and try again, or try to find that installation package 'Adobe

Photoshop CS2.msi' in a folder from which you can install the

product Adobe Photoshop CS2.

                                        OK