why is the itunes store saying my un or pw is incorrect when its not?

We are fellow users here on these forums, you're not talking to iTunes Support nor Apple.

I assume by 'my un and pw' you mean your iTunes id and password. If you do then you can redownload items directly on the iPad. If you aren't already signed into your account on it then you can sign in via Settings > iTunes & App Store and what can be redownloaded for that account will show in the Purchased tabs in the App Store and iTunes store apps on it - music, films and/or TV programmes can't be redownloaded in all countries (audiobooks and ringtones are one-off downloads), and content providers may also have removed their items from the store, so not all purchases may show.

To do it on a computer's iTunes, you can sign into an account via the Store > Sign In drop-down menu option (if an account is currently logged in then you will have a Store > Sign Out menu option instead)

What can be redownloaded for the account will show under the Purchased link under Quicklinks on the right-hand side of the iTunes store home page :

You can then sync themto the iPad

Redownloading an account's past purchases may tie that computer or device to that account for 90 days : http://support.apple.com/kb/HT4627