I actually gave up trying years ago because everything I read basically said, "Don't bother...humans can't comprehend it." Then I read Rrhain's comment, which gave me a whole new lease on life regarding the subject.
Are you ready? This is where the fun starts.
First off, I really don't think that rrhain can imagine 4d, or 5d. What he is seeing in his head is nothing more than 3d folded over a few times. But I may be completely wrong, it may in fact be possible for rrhain to imagine 4d. I would love to discuss it with him, but I don't think I would be on his level, I have to study up a little more. Plus me a rrhain have never had a rational discussion.
But there is one question I have for him, and one thing I would like to share with you. I think one thing that may help you along in your little journey is this.
Picture round pipe(cylinder), 10" diameter, 3' length, Then a round pipe 6" diameter 2' length intersecting the first pipe in the middle at a 45 degree angle. See picture to get a visual:
If you can, without looking it up in a book. layout the shape of the hole that will be in the larger pipe. Never mind the pipes themselves. The amount of triangulation that is needed will start to give you the perspective I am talking about.
Go in the opposite direction. Try to look at something 3d, and see it as 2d. You see, I am a not a college grad, but I am an accomplished sheet metal layout mechanic. Top 5 in NYC. I can cover anything in metal, or look at any 3d object and immediately know how to form it from a flat sheet of metal. I actually invented trig out of necessity. I never learned it in school. A few years after I made my formulas, I read it in a book, and recognized it as trig. I made formulas that allowed me to figure out other sides of triangles, with only knowing the angle of one corner, or the length of one side. This helped me lay out certain stuff. I used to make a lot of custom things for the hospitals, in the operating rooms.
Something happens after years of trying to do this, and I can see how our 3d world is constructed, and actually fold, and unfold it in my mind. This opens up a mental doorway.
I read some of the links provided here, and it was my understanding that the 4 dimension does not have time. Since time = distance, then we would loose all points of measure, and not see things as boxes or any of those silly java scripts in those links. It was once explained to me as being inside a 3d box, looking out one end, and actually seeing your back.
I had a vision once, that I described in detail here:
Consciousness and Dreams
In the vision, I believe what I saw was 4d, although I was constrained to not move about it. It was almost like looking through a glass jar filled with water, but without any distortion. There was no front or back. I wonder if this resembles what rrhain sees in his head.
Anyway, I just rambled a lot here, I hope it makes some sense. I am not an authority on 4d, I possess the same desire as you to be able to see it.