HD upgrade advice needed

[Michal the Milkman]

Here's one for the collective experts,

It's my turn to get a WD Cavier 120 for my cube. I ran Carbon Copy 
Cloner and everything looked good along the way but I just can't boot 
from that new drive. It could be those jumpers or it could be a problem 
with the system. I did change the startup disk in System Prefs before 
moving on with the install and I get a flashing ? for a few seconds 
while the cube searches for the system.

For the moment, I'm running with the original HD where the CD would be 
and the power cable pulled from the new HD, which is already installed 
in the cube. When I have the power on that drive, no combination of 
jumper positions on either drive seems to boot. I've got an iMac also 
running Jag, should I try booting the cube in Target Disk Mode and... 
not sure what actually. Is there a Jag startup CD?

Hoping to move past this so I can install a PL 1Gig card. Apple's got 
my number: digital video, digital camera, new used iPod... I hit the 
Cube's limits quick with all these toys.

Thanks in advance guys and gals,