The Microsoft Exchange Information Store Service may not start automatically when the computer starts. If you try to manually start the Microsoft Exchange Information Store Service, you may receive the following error message:
Event Type: Error
Event Source: MSExchangeIS Event
Event ID: 5000
Time: 5:04:22 PM
Description: Unable to initialize the Microsoft Exchange Information Store service. Error 0x80040154.
This error happen if you have problem with SMTP component in IIS either missing or corrupted.
To solve this problem you have to Reinstall IIS and exchange 2003..It is easy one just follow MS KB326305
and everything will be fine.