A Curious Case Of Data Corruption

Dear group,

if someone could give me an idea what is going on in one of our
databases, this would really really be helpful.

We have two tables with around 2 / 3 million rows. These tables have no
key and no ID. (This major design flaw will be overcome in some later
version of the application-software working on this DB but right now i
have to live with this).

Now for the funny bit

1) I open one window in the Query-Analyzer and write some code like
Begin transaction INSERT INTO TABLE COMMIT
2) in another window i write "SELECT COUNT(*) from TABLE"

If I perform the insert then afterwards select count(*) the row-count
is incremented by two whereas the Insert-Statement said "1 row(s)
modified.

DBCC gives no errors.
DBCC gives amount of rows 2 million rows
Select count(*) on the same table gives 3 million rows

Exporting the data, truncating the table re-importing data gives no
result, right now the DTS-status is 203 and the machine is "thinking".

Is there any possibility to check the "integrity" of the table?

This problem is on the production machine, but right now i am working
on a copy so it was propagated with backup / restore-mechanism.

Any hint would be very helpful

Thanks and Greetings

Uli