Hi Carlos,
Earned Value Analysis (built into Project 2003) allows you to review this information by comparing planned work (Budgeted Cost of Work Scheduled or BCWS) against actual work (Actual Cost of Work Performed or ACWP) and amount earned or Budgeted Cost of Work Performed.
There is pretty good help in Project for earned value data. Be aware however, that in order to calculate earned value data, you have to have the following:
Resources with standard rates (many use $1 or local currency)
Resources assigned to tasks to generate work
Baseline saved
Updated status date.

Even without the complications of earned value, if you have saved a baseline you can easily see:
* when you had planned on starting each task (Baseline Start),
* when you had planned on finishing the task (Baseline Finish),
* what your estimated duration was (Baseline Duration),
* how much work you estimated (Baseline Work) and
* what your initial cost estimate was (Baseline Cost).

If you track actuals, Project will also automatically calculate Start Variance, Finish Variance, Work Variance, Duration Variance, and Cost Variance by comparing baseline data against actuals.

I hope this helps.

Julie