I am somewhat familiar with what you're trying to do as I have do it for my RL job though I only have a couple of years formal experience so there are probably people here who can tell you more. =P I work with indesign though, but I have used scribus on occasion. Couldn't tell you anything about quark.
It's basically a bit arty. As though you were making an old paper or parchment-like thing as the background for a map. That's pretty much it. There are many tutorials out there for making such nice paper backgrounds so I'd take a look at those. They are a good starting point. HOWEVER, there are some important things to consider.
If it's for print it will need to convert OK to CMYK. Most things do but you will get a slightly colour variation if you did it in RGB first. In the past I have worked in RGB before converting it to CMYK and doing colour adjustments later. This is because I mostly do drawing and illustrative stuff for my employer and it's just how I work a lot. It's not optimal but we make it work.
You need to make it at a resolution of at least 300 dpi in either A4 or US Letter. Generally. (you might be doing a different sized book but those are typical) Also you are working on spreads most of the time if it's for print but that just means you'll have a mirrored version of what you're doing. If you don't do it at a high resolution, you will see the pixels when it goes to print. Even if you have a really good printer. Particularly if you do because they will give them more definition.
If you look at that pathfinder page background, you'll note that most of detail is on the edges. The main bit is quite bright and washed out and you can't see a lot of detail at all. They are basically going for black text on a light background so you need to make sure your page isn't actually that dominant, at least for the main content portion of the page. It actually needs to be very subtle and not draw the eye, just make you go "ooo, that's pretty" when someone opens up the book. So apart from your page margins, you will be working in very light colours. Otherwise it is going to look terrible.
I can't really link you to a tutorial though. Most of what I've come across is "in the field" so to speak. But I hope some of those principles help.
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