Well, wine has come quite a long way from when it was first started, you would be surprised. But when I use SCAR 3.06, i would try starting the script (Wizzup's Essence Miner, leetest of them all

), and it would just close. The error was something about freeing an X pixmap. But what I was hoping to do was have SCAR scripts work natively in linux. There are two problems, though: 1, is that the source is closed, so that makes it harder to port. 2, is that it's written in delphi, and there's no delphi for linux. (there's Kylix, but it's just a piece of crap) So I'm going to use C++ and start from scratch.
I like your idea of taking advantage of the multiple sessions. it would be much more efficient using 20 sessions than using 20 "Windows-XP's-Inside-It's-Own-Virtual-Machine"s. The only problem I'd have with that is with runescape itself, not letting you have more than one client open. It's not impossible, though. I remember using a program called XClient that allowed you to dual login.
I also found ways in linux to get colors in pixels, and partial screenshots, so I'm done researching and I'm now actually starting on this project. I'm just not sure what type of licence to put this under. I want to make this open-source, but since SCAR isn't, I would think that would make too many problems.