Missing division

We have installed drupal 6.1 on windows around two weeks back. I created page. In the body of page I have a division tag to align text to left. It is displayed properly. Two days back we have installed drupal 6.1 on Linux. I see following problems.

1. I think Drupal is changing div to p tag in Linux version. So I dont' see css defined for div tag.
2. There are more blank lines in linux version.

I have verified same filter settings or I could be wrong noticing anything. Do you know how to make Linux version to not to change div tags and not to create blank lines?

Is there anyway to find exact version of drupal (Both are 6.1 , but if there is any sub version or date of build etc.

Appreciate your help.
Chinni