Booting and debugging Linux on IXDP425

Hi there,
I am trying to get Linux to boot on an IXDP425 board (Intel IXP425
development board) with no luck. I have Redboot running OK, but when I
load zImage and ask Redboot to run it with "exec" it locks up and
nothing happens (no "uncompressing..." prompt or anything). I'm using
the Snapgear Linux distribution. I have tried a precompiled Linux
image from the Gatewaymaker project
(http://gatewaymaker.sourceforge.net/) and get the same result.
What I'd like to do is step through the Linux startup code with my
debugger, but I have a few questions about doing this.

I'm using a home made "Wiggler" parallel port JTAG adapter. This seems
to work fine (although I have to run OcdLibRemote on a Windows PC)
with GDB for small simple programs (I used it to load my program that
programmed Redboot into the Flash), but I cannot connect to the target
and make it run Redboot (either out of ROM or RAM). Surely I should be
able to connect to the target with GDB and the Wiggler and just tell
it to continue and have it run Redboot?
If I try to run Redboot from Flash with GDB and the Wiggler I get a
"Target Bus Error" from OcdLibRemote as soon as I single step on the
first instruction at 0x0.

The other thing that confuses me is how to make sure that my Linux
image is located correctly. The latest version of Redboot for the
IXDP425 seems to want to run Linux from 0x6000000. As far as I can
make out I should be able to edit vmlinux.lds to make sure that it is
built to load there, but that doesn't make any difference and there
are several vmlinux.lds files (which one is used, arch/arm/vmlinux.lds
or arch/arm/boot/compressed/vmlinux.lds ?).

Any advice would be greatly appreciated.

- Charles