Populate Cell in Workbook 1 if Column B value if present in Workbook 2

I have never worked with these kinds of Excel commands, so if someone can walk me through this step by step, I'd really appreciate it.

Here is the scenario:
I have workbook called Leads_2013-0215 it has about 10K records
I have workbook called LawFirms it has about 4K records.

If the value in Column I in Leads_2012-0215 is present in column G in LawFirms, I want to add the value Law Firm to column AV in Leads_2012-0215.

How do I do this?

Thanks for your help,
Lynn

Thank you Martin. It kind of worked. It put LawFirms into all of the rows where it belonged and into a several where it didn't. I used the drag feature to copy the formula into all of the cells. That might have been the issue, because as you know, it automatically adds one to the numbers in the formula. I know that I can select the copy value rather than the insert sequence command when the paste options appear, but they didn't appear. So, it was a user error, not a formula error.

Anyway. when I QC'd it I realized that there was another way to determine which were law firms, so I fixed the errors.

Thank you for your assistance.
Lynn