What format is the data currently in?
If its in csv or some similar delimited format than it should be a breeze.
I run XP and the "new" version of notepad has the replace tool added to it, so if I need to do a massive data drop I create the sql for each line within notepad and then paste it into the text field in phpmyadmin
alternatively, save it as a file and browse to it.
Either way, your sql (per line) needs to end up looking like this:
INSERT INTO tablename (fieldname1, fieldname2, fieldname3) VALUES ('data1', 'data2', 'data3');
so with my csv file, I'd open it in excel and insert 2 columns, a new column A and a new column Z (or whatever is the last).
Then I'd enter a daft character into every cell in that column, eg # or ~ (ensure it doesn't appear anywhere within the data) and the two columns need 2 different characters inserting.
Now I save back to csv (you need to ensure there are no commas within the data aswell, unless you choose a different delimiter character)
Now open up your csv file in a text editior and replace all your delimiter characters with ', '
Now replace your column A characters with INSERT INTO tablename (fieldname1, fieldname2, fieldname3) VALUES ('
Now replace all your column Z characters with ');
bobs your uncle, as long as you ensure that none of the chars you replaced existed in your data.