Microsoft Project is a project scheduling tool and it does what it does best...it schedules, even when you do not want it to. MSP works of the formula:
Work = Duration x Units, so if you change one, you can affect the others. The first step is to see how you have your defaults set up in MSP. Are your tasks being set as 'Fixed Units', Fixed Work', or 'Fixed Duration'. You really need to know who MSP works to use it effectively with Clarity. The green books are a good resource, and also a few threads on this topic done in the past in the forums. If you send me your email I'll send you a presentation done at the Canadian Clarity User group on MSP.
Also,
Since you are using MSP, are you looknig at using timesheets in Clarity? If so, be prepared for the affect that actuals has on a MSP schedule.
Regards,
Michael
mike@journeyassistance.com