I purchased a ticket from Tokyo to Detroit on Northest that arrives at 1:30PM. I want to get to Houston as my final destination. I was wanting to buy a ticket on Continental from Detroit to Houston.

Can I check in all the way to Houston even though I have 2 separate tickets?

If my Northwest flight is late getting into Detroit do I have any chance that Continental will allow me to take a later flight or will I have to buy another ticket?

Thanks to all for any advice.