fact table is one which contains all the facts
(measures).aggregate table is one which is created after 
the cube is processed.this aggregate table contains human 
unreadable text.

Diff b/w two tables is performance.

Fact tables contains million of records and retriving the
records from fact table takes time.where as aggregate table
contains limited data from all the required tables,and we
retrive the data it takes less time.

Sorry guys i am not sure

The difference that i know is that the aggregate tables 
contain only the summaries of the data where as the fact 
tables contain summaries and measures. i.e.,the grain of 
the data present in fact table is more than the grain of 
the data present in aggregate tables.

A fact table typically has two types of columns: those that 
contain numeric facts (often called measurements), and 
those that are foreign keys to dimension tables. A fact 
table contains either detail-level facts or facts that have 
been aggregated. Fact tables that contain aggregated facts 
are often called summary tables or aggregated fact. A fact 
table usually contains facts with the same level of 
aggregation. Though most facts are additive, they can also 
be semi-additive or non-additive. Additive facts can be 
aggregated by simple arithmetical addition. A common 
example of this is sales. Non-additive facts cannot be 
added at all. An example of this is averages. Semi-additive 
facts can be aggregated along some of the dimensions and 
not along others. An example of this is inventory levels, 
where you cannot tell what a level means simply by looking 
at it.

hi,

   The difference might be in the granularity level....

fact table has measures and aggregated data .Aggregate table
has only aggregate value (ie) precalculated value.

Aggregate tables also known as summary tables, are fact 
tables which contain data that has been summarized up to 
different level(Month level, year level) of detail 
aggregation.

The main difference is the type of involvement in Schema

Fact tables generally contains measures and the composite 
key, which is generally a combination of foreign keys from 
the respective dimension tables.

Aggregate tables are summary tables which contains the 
summary information say for eg:total sales revenue (for a 
quarter).

So the difference is in the granularity.Fact tables store 
date in more detail level, but in aggregate tables the 
granularity is high.