But I set in Mac OS X to startup in 9 but how do I chnage it back to start back up in Mac OS X?
9.1 and later have a version of the Startup Disk control panel that can see Mac OS X... I don't think the Startup Disk control panel that came with 9.0-9.0.4 could do this.
Having both on the same partition shouldn't be too much of an issue (just try not to use the root level of that partition for file storage and the like).
I haven't had too many issues like your having with my Wallstreet though. But than again, I was going from Rhapsody 5.6 to Mac OS X v10.2. I have installed Mac OS X Developer Preview 4, Public Beta, 10.0 and 10.1 on it, but all for very short periods (and on disks that were 8 GB or smaller, I have a second drive where my battery used to be for additional storage).
In other words, I'm trying to recall my experience with 10.1 from a brief encounter with it on my Wallstreet many years ago. Sorry if it is not much help.
On a side note (not really related too much to this topic), I only tried a larger hard drive in my Wallstreet once. The drive created a magnetic field which triggered the hardware sleep switch and was unusable (there are tricks around this, but I opted for two hard drives instead). As I recall the primary manufacturer of drives that cause this issue was IBM.
Just in case some one comes across that issue.