Error message in Outlook

"to free up disk space, outlook express can compact?

That message is issued by Outlook Express, not by Windows. So you have
OE getting loaded when Windows starts up. Use msconfig.exe or
SysInternal's AutoRuns to find out where you added OE to the list of
startup items. Maybe you put a shortcut to OE in your Start -> Programs
-> Startup folder.

"Outlook Express which was infected"

 1 - Download SpyBot Search and Destroy.
http://www.spybot.com/en/index.html
It is freeware that even the government permits to be installed on their computers. After downloading, install, and get the latest updates. Then, (for best results) restart windows in Safe Mode WithOut Networking, and run Spybot - have it scan for issues, and let it fix any issues it finds. Reboot and try to use Outlook Express. (If it still doesn't load you may need to remove that windows component and then reinstall - kinda tricky)

2 - Get a good Anti-virus program that can find and combat the worm (I cannot make any specific recommendations, but here is a free one: http://free.avg.com/

3 - If you have a backup restore image of your primary partition, use your appropriate software to restore to your last known safe backup of the primary partition.

4- Use windows installer/recovery to recover windows to it's last good known state.

5- Backup all your data files to an external hard drive and reinstall you operating system (windows)