installing SW2005sp0 with XPsp2

you have instructions

Windows Installer error

The Windows Installer service could not be accessed' on Windows XP?

When you attempt to install a program that uses Windows Installer, such as Office XP, you receive: "The Windows Installer service could not be accessed. This can occur if you are running in safe mode or if the Windows Installer is not correctly installed. "

This error is probably the result of a damaged registration service. To resolve this issue:

1. Open a CMD.EXE prompt.
2. Type msiexec /unregister and press Enter.
3. Type msiexec /regserver and press Enter.

I thought SW2005 wasn't compatible with XPSP2 until SW SP1?

Len

Solidworks is, but the driver for the security dongle (if you have the misfortune to require one) isn't. You'll have to uninstall Swx completely, clean registry, get the latest dongle driver from Aladdin, then reinstall Swx.