New install. Partioning advice please.

[Nat Gross]

Hi;
On a new FC3 (or FC2) install, on one hard drive, how do I set it up so 
that certain directory structures do not get erased when installing to a 
future version of Linux?
And as a follow up question, can I re-partion an existing fc2 system, to 
allow the same?
I wasn't aware that this was possible, but the FC-3 install notes allows 
for reading the iso's "from a hard drive location not overwritten by the 
installation", which prompted this question. This would prove extremely 
useful of course, not only for the purpose os install iso's.

Thank you much;
-nat