I do not have experience loading more than one IOS on a router, but what I would do is download a tftp server program (try Google), unless you have one. Run it locally on the computer that is connected to the router via console. The tftp server program must be running in the backround. The program should give you a option to see where it puts files on your hard drive. Then, make sure the new IOS is in the same directory that the tftp server program specifies. You must first establish connectivity betwen the router and the computer via ethernet or fast ethernet, whichever your router has. I believe it has an ethernet miniswitch built in with fast ethernet interfaces. So, connect the computer to the fast ethernet intrface and configure it with an ip address on the same subnet as your computer, and temporarily assign a statip ip to your computer on the same subnet. Then you are ready to upgrade, and the command sequence in the router is as follows...
router>en
router#copy flash tftp
This will back up your current flash IOS image to the hard drive of your computer in case something bad happens. Bad idea to not back it up!!! It will ask you the name of the flash image you want to copy to the tftp server, so you may want to do this
router#sh flash
and write down the name of the biggest file---should have .bin at the end. Then, to copy the new image,
router#copy tftp flash
It will ask you for the address of the remote host, which is your computer, and then the name of the flash image on your hard drive. First it will erase the present image (don't worry---you backed it up, right? RIGHT??? Good.). Then, it will copy the good one you specified and reboot, then you are good to go. Good luck.
Tim