Multiple FreeBSD-installations on one harddisk?

[a at jenisch.at]

In order to run two (different) versions of FreeBSD on one Harddisk
(4.9 and 5.2) are there any special caveats/pitfalls besides having a
separate slice for every installation?

Anything special to take care of during installation (esp. when
installing the second FreeBSD?)

Is it possible to use the same swap-partition for both instances of BSD? 

thanks much in advance for your help,
-ewald