I agree with donnybrook. Do as much of your IFR training in a small fixed-wing as you can because IFR is IFR - the platform isn't that important in the early stages. A fixed-wing is cheaper and more stable and will make grasping the basics so much easier and a whole lot cheaper (just don't tell your friends you flew a fixed-wing). Self-study is a good way to cut costs but there are strengths in studying in a structured group environment. You will have lots of questions in the beginning and its nice to hear other's questions as well...and hearing the correct answers from an experienced instructor.
I used Culhane's when I did my INRAT and, as Phil said, you need a fairly solid background in instrument procedures to use it as sole source guidance...not for an IFR newbie unless you want to use it to crosscheck your knowledge.
Computer-based sims are great for putting theory into practice before you fork over the big bucks to fly them in the actual aircraft but be sure you're doing the procedures correctly before you imprint any bad habits. IFR is largely procedural and bad habits are hard to erase once they've been practiced a lot.
Training for IFR at night is great advice after you've gotten some of the basics under your belt. Reading approach plates by flashlight isn't great when you're starting out. Outside visual cues are usually a bigger distraction than a benefit (they can really contribute to "the leans") so night flight takes away that problem and many times you can even fly without the hood. There may be less traffic at night as well. Also, find a school that is willing to do actual cloud time...its a whole different ballgame than hood time.
Find a good IFR checklist that includes enroute procedures and use it. Memorize things like the level-off check and pre-descent check so you can be thinking well ahead before level-off or descent. Cockpit management is so important when operating IMC so strict checklist usage is critical to success.
Enjoy. Flying under IFR is challenging and a well executed flight is extremely rewarding. Its money well spent.
