Bootcamp question: How to update the Windows on my bootcamp made flash memory?

Hi,

Previously Bootcamp helped me to make a flash memory that was an automatic Windows installer along with bootcamp drivers, it went well with installation and I was halppy. Until I noticed strange crashes at Windows and as I trust Apple, I thought it was a crappy Windows image.

So I recently purchased a newer Windows 7 image and want to try it out and I have two questions:

1- To prevent downloading 1+ Gb of bootcamp windows driver downloads, how can I make another bootcmap-made Windows installer flash memory with my newer Windows image BUT copy Bootcamp drivers from previous one?

2- How I should install the new Windows over previous one without corrupting Mac partition and other stuff like MBR?

Thanks.