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I’d suggest installing phpMyAdmin locally and importing your database with that or you could use a desktop database management application like SQLYog.

You’ll need to update any references to your live hosting url (domain.tld) in your SQL file to reference your local dev url (localhost.localdomiain).

Also, if you’re running under Windows and have WPMU set to use sub-domains you’ll need to add entries for each subdomain in your hosts file manually.

Andrea Rennick over at wpmututorials.com has just written a pdf ebook on installing MU that you might find helpful too.

You could update the file size limit in your php.ini file although that will increase the upload limit globally, not just for phpMyAdmin.

upload_max_filesize = 5M;

memory_limit = 16M;

A preferable approach might be to add an .htaccess file in your phpMyAdmin directory with the following directives:

php_flag upload_max_filesize “5M”

php_flag max_execution_time 300

php_flag memory_limit “64M”

This should increase your file upload size limit just for phpMyAdmin to 5Mb and allow for the extra execution time required.

It’s worth noting that most sources suggest increasing php’s memory limit from the default 16Mb’s when using WordPress MU anyway so you might want to make that change in the php.ini rather than the .htaccess file.