You are limited to adding around 500 keywords per time using the normal way.
There is a way of getting your Google campaigns into MSN but I found it was too much of a pain so I done my the manual way.
---- Let me know if this does not work and I will look again ----
Click the Campaigns tab. If you have more than one campaign, in the Campaigns table, click the name of the campaign that includes the order you want.
On the Order List page, in the Order name column, click the order you want to work on, and then do one of the following:
If the order is Submitted or Paused
Click the Keyword Performance tab.
Click Manage Keywords.
In the Add multiple keywords drop-down list, select Import or Export keywords.