Your previous problem was nothing to do with "saving the softmod to right partition"...... You chose to use a softmod that has lots of newbie-unfriendly options, installed it using options that meant that mistakes were likely to be catastrophic, then proceeded to make lots of mistakes.
To install a different disk into your old Xbox you need to be able to copy files (the right files to the right places, not in a random sense) to the disk and lock it - and with only a laptop you can't do that. If by old Xbox you mean the one you screwed up a few weeks ago then you could possibly hotswap to a USB/IDE enclosure and use Xplorer360 beta 6 to install a clean dash then redo the softmod, or you could fit a chip.
To mod your new Xbox, make sure that the MS Dash is version 5960, and if it isn't use Halo 2 to update it - as I described in your original post. Then use the Krayzie 1.1.1 gamesave softmod installer to install the softmod - select Basic Install - UnleashX Dashboard. Once that's done use HeXEn to update the dash, install XBMC etc. You can also use HeXEn plus a separate IDE power supply to build and lock your larger hard drive, or you can use Chimp 2618 to do that with the Molex Y splitter.
Also, FYI, with a softmod you have no choice "about places to install the latest Xbox dashboard" or about where to put the MS Dash - the MS Dash location was decided by Microsoft, and the hacked dash location is decided by the person who wrote the softmod.
This post has been edited by Heimdall: Jul 18 2011, 09:16 PM