When will OS X ship with new iMacs?
I imagine that OS X will start shipping with new Mac shortly after the final release of Mac OS X, which is slated for early next year. Note that it may take some time for dealers to clear out inventories of computers that came with Mac OS 9 preinstalled.
However, in the past Apple has allowed users who buy a new Mac after a new OS is released (or a few months before), but received the older version, for a significant discount. I took advantage of the program for my Power Mac G3 (platinum) to update from 8.1 to 8.5, and I think it was around $20 with shipping.
will OS 9 users be able to upgrade?
Yes, if you are using a computer with a G3 or G4 processor. The current Mac OS X Public Beta actually requires that Mac OS 9 already be installed in order to run Classic applications in Mac OS X. As a Mac OS 8.6 user, I'm hoping that the final release of OS X will include all of the components of OS 9.
Can Adobe Photoshop for Macs open .tiff and .bmp files?
I cannot say for certian as the one time I have used Photoshop was on a Windows 95 PC, but I imagine that it can. If Photoshop does have problems, download the shareware GraphicConverter (which I know can read TIFF and BMP images, along with virtually every other image format you've ever heard of along with dozens you haven't) from http://www.lemkesoft.de
and use that to convert the images to a format that Photoshop can read.