Total confusion between 过 and 到

Last night's lesson left me with brain ache... my Chinese teacher was trying to teach us when to use 过(guo) and when to 到 (dao) when talking about past actions, but even after a 2 hour lesson I felt just as confused. I don't think her teaching style helps much, as she has a horrible habit of glossing over questions the class raise, but answering really quickly and moving on... almost like she finds students asking questions disruptive. Going home and trying to get my fiancé to explain the differences wasn't much use either, as he inherently knows when to use both, but couldn't really clearly explain why (and I think he was relishing the opportunity for him to have the upper hand and know something I didn't, as it's usually me correcting his English). The night ended in me moaning that Chinese is sooooo confusing and going to bed with 过 and 到 swimming around my head...!!

I *think * the difference is that 过 should be used in a "have you ever" sentence... for example:

你买过这本书吗？ Have you (ever) bought this book?

Whereas 到 should be used when something has just happened recently... such as:

你买到这本书了吗？ Did you buy this book?

I'm still not 100% sure if I'm getting this right though... if there's anyone out there that can explain the differences between guo and dao a bit more clearly, leave me a comment! I'll be eternally grateful!!