Have you looked at launchd, the new all-purpose task control daemon? Don't be put off by the fact that it's from Apple--it's open source, licensed under the APSL, which I believe is GPL-compatible, if you care about that kind of thing. It seems to offer many of the features you want, including task scheduling, preemption control, etc.
http://developer.apple.com/documentation/Darwin/Reference/ManPages/man8/launchd.8.html
http://www.macgeekery.com/tips/all_about_launchd_items_and_how_to_make_one_yourself
@corlin Ooh--hang on--requires mac? No good for our environment, alas. We're on solaris now. Could conceivably do linux, but windows is probably most preferred.
@corlin Never heard of that--will take a look. Thanks!