You are changing OS and you cannot "migrate" to Windows from anything else. V9.1 is no longer supported, so I would not even consider it. What you are going to have to do is use db2look and db2move to "migrate" the data. With this in mind, you can move to any version, so go with the latest (10.1 for now).
Here is what you should do:
1) run db2look on the AIX system.
2) modify the output to conform to Windows and take advantage of new Version features
3) create the database (tables, etc) on windows using the result of step 2
4) use db2move to copy the data to Windows.