cant connect dongle to xp

Are you sure it's compatible with Windows XP, and if it is, have you got the final service pack from Microsoft (SP3) installed? If not, download and install it (you need to have SP1 or SP2 installed first).

You can either use Windows Update for online installation of SP3, or download the entire SP3 setup file for offline installation from here: http://www.microsoft.com/en-gb/download/details.aspx?id=24

If your Windows XP is already up to date, pop in to a T-Mobile/EE shop for advice.