need vacuum after insert/truncate/insert?

If I insert a bunch of rows, then truncate, then insert a bunch more rows, do I need to vacuum?  I've been assuming
thatTRUNCATE TABLE is a brute-force technique that more-or-less tosses the old table and starts fresh so that no vacuum
isnecessary. 

Second question: Same scenario as above, but now the table has indexes.  Is a reindex needed, or are the indexes they
"truncated"too? 

Thanks,
Craig