The Perl-XML FAQ has a
section on encodings.
When you parse a file, the resulting data in the Perl variables will be UTF8 encoded regardless of the source encoding. I'm not an expert on mySQL but I wouldn't have thought that the act of INSERTing into a table would result in characters being converted from UTF8 to ISO8859-1.
With Perl 5.6.0 and later, you can convert a UTF string to a latin-1 string with the somewhat cryptic:
my $latin = pack("C*", unpack('U*', $utf));
As jkahn said, it's not possible to map all UTF characters to Latin-1. In particular, the 'smart quotes' characters from MS Office apps do not have Latin-1 equivalents. You could simply encode characters beyond 0x7f as numeric entities (if you're ultimately going to write them back out as XML or HTML) or you could replace troublesome characters with more generic equivalents. The FAQ has some code snippets for both options.