Unnecessarily long query process time

[Augey Mikus]

On one of my MySQL servers (Dell PowerEdge 800Mhz w/ 512MB RAM), I have 
a couple tables that have about 3 million records in each. However some 
of the records in the tables are duplicates of each other. Here is a 
query that should return the number of unique records for both tables:

select count(*) from table1,table2 where table1.value != table2.value;

However, this query has been running for more than 40 hours and still 
has not finished.  Is this normal?

Thanks,

Augey