Database is unstable after upgrade

We recently installed a new database server. In the course of migrating to
the new box we also switched from postgress 6.5.0 to 6.5.3. 7.0 was
released a few days after the upgrade.

Since the upgrade we have had three problems:
1) The database seems to be running slower, this is admittedly subjective.
2) A weekly vacuum has died(Twice in a row) and I had to delete all the
indexes, recreate them and rerun the vacuum.
3) One large table became corrupted and could not be vacuumed. I could not
dump it even after recreating the indexes. Fortunately this table was not
critical. I restored from a backup and its is running fine at the moment.

I have been thinking of moving to a nightly vacuum which might elimiate some
of the problems.

I have two questions: Are there any known instabilties that might have been
introduced between 6.5.0 and 6.5.3?

What are the chances that upgrading to 7.0 will fix the problems?

FYI the old hardware was a dual PIII 450 with 1GB Ram, one LVD SCSI disk for
the database and one IDE disk for everything else. The old box was also
running a secure web server. The new box is pretty much the same hardware
except both disks are now LVD SCSI's and it is a Dual PIII 600. The secure
web server stayed on the old box to further reduce the load on the database
server box.

Other than these problems the new hardware has given me no reason to think
it might be flakey.