If money weren't an issue, I would probably have the following:
-Apple Powermac G5 Dual 2.0 GHz (though I might wait a few months for the 3.0 GHz ones destined for this summer), complete with 8 GB of RAM, a Superdrive, and four hard drives.
-Apple Powerbook G4 15"
-A homebuilt Pentium 4 3.06 GHz with HT, triple-booting between Mandrake Linux 9.?, Red Hat Fedora 9.?, and Windows 2000 Pro.
-A homebuilt AMD 64 machine, triple-booting between Slackware Linux, Debian Linux, and Windows XP 64-bit Edition.
So from your list, I'll have to take the G5.