automagic way to (re-)install all packages on a system?

[Jeff.Hodges at KingsMountain.com]

Here's a scenario..

I'm wondering if there's an automagic way to re-install all packages that are 
installed on a given "source" system -- e.g. have synaptic or aptitude write 
out a file of a system's current set of installed packages, then be able to do 
an ubuntu install on a new "target" system, say, and then feed that file to 
synaptic/aptitude/whatever, and have all the packages that'd been installed on 
the source system installed on the target system.

I've poked thru the man pages and help files and maybe I missed it, but I 
didn't see anything that looked like it unequivocally satisfied the above 
scenario.

Is there a (straightforward) way to do this?

thanks,

=JeffH