vacuum won't fix tx wraparound problem

I'm getting the following errors and I'm not quite sure what to do at this point. The database is very large and I
can'tget it to accept commands. Please help! 

maindb =# create table test1();
ERROR:  database is not accepting commands to avoid wraparound data loss in database "maindb"
HINT:  Stop the postmaster and use a standalone backend to vacuum database "maindb".
You might also need to commit or roll back old prepared transactions.

[root@P00C01S01-DBM04 data]# su postgres
bash-3.2$ postgres --single -D /data1/pg2/home/data -O maindb
 -  - 2010-06-27 13:07:05 UTC :WARNING:  database "maindb" must be vacuumed within 1000000 transactions
 -  - 2010-06-27 13:07:05 UTC :HINT:  To avoid a database shutdown, execute a database-wide VACUUM in "maindb".
    You might also need to commit or roll back old prepared transactions.

PostgreSQL stand-alone backend 8.4.4
backend> vacuum
backend> ^D^D
exit

# psql -U drdb maindb
psql (8.4.4)
Type "help" for help.
maindb =# create table test1();
ERROR:  database is not accepting commands to avoid wraparound data loss in database "maindb"
HINT:  Stop the postmaster and use a standalone backend to vacuum database "maindb".
You might also need to commit or roll back old prepared transactions.


I also reset the transaction log aftwards which didn't help. Any help would be appreciated. Thanks

--Gene