There is not a way your phone can be locked just by adding ringtones and themes (not to my recollection that is, but i truly doubt it).
As for iTunes when u plug in your phone click NO you dont want to update then it'll have a box that says "dont ask me again" click that. and it wont ask u again. but make sure u never click restore! Now head over to the d/l section and u can find all the apps there try iBrickr first its very very easy for beginners. if u need any more help let me know. Good Luck!