I wouldn't install it on a machine that has a BIOS date more than six months or so old, especially if you are running a recent-stepping P4 chip in it. I also wouldn't feel the need, if one already had an existing anti-virus/anti-spyware/firewall solution, and didn't want to encounter the performance overhead of the software DEP that is present as part of the binaries in SP2, and cannot be disabled (Well, the overhead cannot, the exceptions resulting from a software-mode DEP exception probably can be.)