Need a way to unpack and repack a big executable!

[crispy]

Do a search (e.g. google) for "programmers tools" etc.

You should find stuff like PROCdump etc, but their use and help on 'em is a little beyond this forum. Just search around for help files/tutorials. There are plenty about if you look.
There are of course other ways of doing that by using breakpoints in SoftICE, but again there are plenty of tuts available.