Q: My laptop has gone very very wrong, I need tu uninstall itunes and reinstall, will I lose my purchased downloads?

Deleting and reinstalling iTunes won't remove your library from your laptop. But depending upon what you mean by 'wipe my laptop' (are you going to remove all content from it ?) then you might do so - do you not already have a copy of your downloads/library on a backup ? If not then you can't access to computer's iTunes hard-drive to be able to take a backup ? By default your library is stored under \Users\username\My Music\iTunes on Windows 7.

If you are going to delete everything from your laptop then you may not be able to redownload all of your past purchases - music, films, tv shows can't be redownloaded in all countries ; audiobooks and ringtones are one-time only downloads. And there is no guarantee that any previously purchased item will still be in your store for redownloading, content providers occasionally remove their items. What you can redownload will show under the Purchased link under Quicklinks on the right-hand side of the iTunes store homepage (and check to see if anything is hidden : http://support.apple.com/kb/HT4919)