The release notes indicate I should be able to run RoundCube 1.0.0 on my server with PHP 5.2.1+, but I get the error:
QuoteMySQL driver requires PHP >= 5.3, current version is 5.2.17
My web host does not have plans to upgrade PHP very soon.
Is there any way I can complete my upgrade without 5.3?
If you use MySQL you have to have PHP 5.3 or greater. You can use Roundcube on PHP 5.2.1+ if you use a different database like PostgreSQL.
Maybe you should just change the host. http://php.net/eol.php