Scribus is an open source (free to download) application that emulates the workings of QuarkXpress working under Apple's X11 Window (i.e. it is a UNIX/Linux piece of software).
Scribus is good. It is comprehensive yet simple to use once the slightly different controls are understood. The emulation of QuarkXpress is excellent and it qualifies as a high end Desk Top Publishing application in that it offers accurate and rock solid placement of individual items on the page.
But there are significant drawbacks. Getting it loaded takes a lot more savvy than an average Apple user is accustomed to using during installation. The X11 Window is different and is limited in a number of ways. For example, I could find no way to access files on a second hard drive or indeed outside my user's folder. Color selection is archaic and color management looks like being several light years behind Apple.
I had a serious number of freezes at one stage but eventually managed to work my round past the bottleneck. Fortunately Scribus has an autosave function which I set to every five minutes to minimize data loss.
Printing is straightforward but the controls are not as comprehensive as QuarkXpress. The export to PDF is, on the other hand, very good.
In the middle of an evaluation exercise Apple introduced iWork and its Pages document processor. It's hard to tell at this stage whether or not iWork is a DTP contender. If it is, it is likely to get my vote. If not, I'm stuck with the thought of buying QuarkXpress for OS X for around $950. This is the point where I start to think again about Scribus! But the jury is out until I get my hands on iWork at the end of January.