Start up problem

[Larry Friedman]

Here's the problem folks, I partitioned my drive out into two volumes. 
One was running 8.1 merrily and I loaded 7.6 on the other. Restarted to 
7.6 and it tells me this startup volume won't work with this Mac (every 
spec I've read says 7.6 should). The problem I'm running into is that I 
can't redirect it back to the 8.1 volume, all I can do is restart to 
the same volume. All I have is an external HD with OS9, I'm going to 
take it home and hopefully it will shift and start up off that drive. 
At start up is there any way for me to force it back to booting from my 
8.1 partition? How about forcing it to start from the external HD?

Thanks

Larry