If you're concerned that it's NIMDA, then look for two things:
1. Determine if you've got IIS installed. If you're running Win2k Server or Win2k Advanced Server, then IIS 5.0 is installed by default. If you have Win2k Pro, IIS is not installed by default, but it can be optionally installed. Open Task Manager to look for the Inetinfo.exe process -- if you find that process running (on the Processes tab), consider yourself vulnerable.
2. To determine if your system has been compromised, look for the following:
* root.exe artifact (indicates a compromise by Code Red II or sadmind/IIS worms making the system vulnerable to the Nimda worm)
* admin.dll artifact or unexpected .eml files in the directories with web content (indicates compromise by the Nimda worm).
Unfortunately, if you are infected, the only recourse is to format your hard drive.
Please, make sure you're running an AV program and update it regularly. Also, installing a personal firewall is a must. A lot of folks use Zone Alarm, but some have also reported having problems with it. I *highly* recommend eTrust EZ Firewall (made by the people who made the Inoculate AV program) along with their eTrust EZ Antivirus program. Both are very good programs, they run very smoothly and do not cause conflicts, and they do not hog system resources.