When you try to install a program, such as Microsoft Plus! for Windows XP or Microsoft Office, in Microsoft Windows XP, you may receive the following error message:
“The Windows Installer Service could not be accessed.
This can occur if you are running Windows in safe
mode, or if the Windows Installer is not correctly
installed. Contact your support personnel for assistance.”

This issue may occur when both the following conditions are true:
* You are using Windows XP in Normal mode.
* The Windows Installer Service that is included with Windows XP is unregistered or damaged.

To resolve this problem, use one of the following methods.

Method 1: Use the Msconfig tool to confirm that the installer service is running

• Click Start, and then click Run.

• In the Open box, type msconfig, and then click OK.

• On the Services tab, click to select the check box that is next to Windows Installer .

• Click OK, and then click Restart to restart the computer.

• Install Office again. When you are prompted to enter the product key, type the product key, and then click Next.

Office will be installed, and you will not be prompted for the product key when the programs start.

Method 2: Re-register Windows Installer

To re-register Windows Installer, follow these steps.

• Click Start, and then click Search.

• Click All files and folders.

• In the File name box, type Msiexec.exe, and then click Search.

• After the search is complete, make a note of the location of the Msiexec.exe file. The location of the file should be similar to the following example: C:\Windows\System32

• On the File menu, click Close to close the Search dialog box.

• Click Start, and then click Run.
• In the Open box, type regedit, and then click OK.

• Locate and then click the following registry key:HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\MSIServer

• In the right pane of the Registry Editor window, double-click ImagePath.

• In the Edit String dialog box that appears, make sure that the string in the Value data box contains the correct path for the Msiexec.exe file that you determined in step 4

• On the File menu, click Exit to quit Registry Editor.
• Start your computer in Safe mode, and then register the Msiexec.exe file. To do this, follow these steps:
• Shut down your computer, and then restart your computer normally.

Shut down your computer, and then restart your computer.

Restart your computer and press the F8 key on your keyboard. On a computer that is configured for booting to multiple operating systems, press the F8 key when you see the Boot menu.

Use the ARROW keys to select Safe Mode, and then press ENTER.

If the Boot menu appears again, and the words “Safe Mode” appear in blue at the bottom, select the installation that you want to start, and then press ENTER.

Log on to the computer.

Click Start, click Run, type msiexec /regserver in the Open box, and then click OK.

I’ve try these two steps and working.

Please let us know, if you have similar problem and can’t be resolved by using this methods.

source : Microsoft.com