There's not a memo control, so to speak. Memo is a data type, not a control type. Assuming your report is based on a table, then so long as the field in the table is set the memo data type, it works.
To test this, make a dummy table called "Test" or something simple. In it, put one field called "TestField" and set it's data type to Memo. Go out to a website or something else where you can get more than 255 characters, dump it into the memo field in the table you just created. Then make a dummy report, base it on the table "Test" and drop that memo field in. It will show the full memo field.
On thinking about this a little, I'm starting to think you have data that is bigger than 255 characters and you're trying to import/write that into a text field in a table. That won't work. Bob is right in that a textbox in a report will handle roughly 64KB of text (~65,535 characters). So long as the underlying field that needs to hold more than 255 characters is set to memo, you'll be okay.
