i have one of these supplied by work so no hacking for me :-( however there are loads of free apps that you can get to using market place, look at the ones it has then slide across to all and got to bottom and tap more...
unfortunately you have to use zune (now that is a rubbish bit of software) to setup sync etc the only thing that it is really useful for is updating the phone to the latest mango release.
settings\about latest should be Software: Windows * Phone 7.5
if it isn't at 7.5 then it is worth the update it takes a while about an hour and DONT take out lead whilst its doing it of it will crash. there is a bit where you get a picture of a phone with a lead going to a pc just go and make another cup of tea....lol
its only when you get 7.5 you can use custom ringtones.