Hello, dear new e-maculation user !
Your question is that kind I can answer :
- JIT (just in time) is a technique to make emulation more efficient. In Basilisk II JIT, this speed up the 68k emulation. This technique is also used by SUN for enhancing JAVA execution speed.
- Despite what you may see around the web, there is NO PPC emulator, nor anything that can allow you to run MacOS X on a PC. Browse this site for more info, its sometime funny
- Don't worry about getting a ROM image, it doesn't hurt the computer. But taking a ROM from a G3 or any PPC Mac is useless (for reasons above). And remeber that legally, you can only take the ROM of a computer you own, because it is Apple's property.
In brief, Basilisk II is a free emulator that allow you to emulate a 68k Mac only. It's the best so don't try the others (except the JIT version, of course

, there are buggy. A big installer is available which will install anything you need : grab it at
http://prdownloads.sourceforge.net/cito ... E?download
Browse this website and the forum, you'll surely find the answers to each of your questions, present and future. Then you will turn into a emaculation expert in emulation and softmac criticism.
Good luck !