TestLink

Hi, I work with a services company in India, and we would like to use Test Link as the Test Case Management Tool enterprise wide. My questions are
1. Has TestLink been used in large installations before?
2. Is there an LDAP intergration, where I can use the domain login to also login to TestLink?
3. How do I upload my current Test Cases which exist in Excel Sheet to TestLink?
4. Is there any paid support for TestLink? Which will help my orgainisation adopt TestLink.

Will be expecting your replies at the earliest.

1. What you mean large? We work with thousands test cases in several projects.
2. There is LDAP authentication support.
3. You can export your data as XML from excel. See documentation and example files.
4. We doesn't offer it formally ... of course there are experienced people who could help you.