Devin,
Take a look at this article...
http://docs.info.apple.com/article.html?artnum=25249
I believe Wallstreet is "PowerBook G3 Series," is it not? I don't have one of those, but I have a tray-loading iMac with the same 8GB boot partition limit. Basically, all OS components must be installed in the first 8GB (or so) of the hard drive due to a limitation in the IDE controller used in these Macs (the ones listed in the article). Normally, the Mac OS X Installer will prevent installation (on the affected Macs) if the target volume is over the 8GB limit. However, since you "bypassed" running the installer on the Wallstreet by using a Mac that supported Panther, it installed fine. In fact, initially everything worked OK because all OS components were still within the first 8GB of disk space. However, when installing QuickTime and iTunes, some OS components must have been placed beyond the 8GB limit. Therefore, you got the gray screen. I am guessing this is your problem.
The solution is to do what the linked article suggests. Partition your hard drive. Instead of setting the first partition at 8GB, it is safer to go a little lower - about 7.5GB. On my iMac the first partition is 7.77GB, and that works. The second partition can be the rest of the available disk space. The second partition is fully accessible and you can runs apps from it (although some app installers complain if you do not select the boot volume). You can also put all your data files (such as your iTunes Library) on the second partition. If you use Classic under Mac OS X, the designated Classic System Folder can be on the second partition. [Note: Booting directly into Mac OS 9 has the same 8GB limit. The System Folder must be in the first 8GB of disk space in order to directly start from it, or you will get the same gray screen.]