Compile on different box?

I have installed MythTV on a fairly low power box.  It will be used as an 
information center and "digital picture frame" of sorts.  No TV recording.  
It is all installed and works fine.  Now I want to add LIRC.

The issue is that this little box has only 128MB of RAM.  It cannot build the 
Linux kernel.  I compiled the matching kernel version source on a different 
box and copied the entire tree over to the /usr/src directory on the 
destination box.  LIRC then compiled just fine with the usual setup.sh and 
make commands.

However, when I do 'modprobe lirc_serial' I get errors:

[root <at> myth lirc-0.7.0pre8]# /sbin/modprobe lirc_serial
WARNING: Error inserting lirc_dev (/lib/modules/2.6.8-1.521/misc/lirc_dev.ko): 
Invalid module format
FATAL: Error inserting lirc_serial 
(/lib/modules/2.6.8-1.521/misc/lirc_serial.ko): Invalid module format
[root <at> myth lirc-0.7.0pre8]#

I have googled on the "Invalid moduel format" error and still have not found a 
clear answer on what to do from here.  Any ideas?

System details:
Fedora Core 2
cat /proc/version output:
Linux version 2.6.8-1.521 (bhcompile@...) (gcc
version 
3.3.3 20040412 (Red Hat Linux 3.3.3-7)) #1 Mon Aug 16 09:01:18 EDT 2004
ZapWay reciever on ttyS0 tested to work on another box.
lirc-0.7.0pre8 as you can see in the error log above.

Alan