How to import the data of postgres 8.x to postgres 9.x
What you need is a dump / restore. However, for this to work, you need the old PostgreSQL 8.4 server running. The new version 9.1 is not binary compatible and cannot use the files in postgres/8.4/data directly. 

If you have no backup and cannot run PostgreSQL 8.4 on your machine any more, you are out of luck. Why is it that you cannot install PostgreSQL 8.4 any more? You'll have to, if you want your data.

On a side note:
It is recommended that you use the pg_dump and pg_dumpall programs from the newer version of PostgreSQL, to take advantage of any enhancements that may have been made in these programs.