=>So far I've located these packages: RR-track, 3rd PlanIt, Cadrail, Win =>Rail, 3D Railroad Concept & Design, Right Track.
Any of these will do the job; their differences are more a matter of working style and aesthetic preferences than anything else -- oh, yeah, a couple have add-on thta allow ypou to "operate" your planned layout on screen. MR had a comparative review a year or so ago; I can send you a _photocopy_ (scans of magazine articles just don't do it for me, and I refuse to make them for others -- my scanner is consumer quality, and that's just not good enough for this purpose.) Drop the first w and the last n in the reply to address to e-mail me.
But be warned: There's a steep learning curve, especially if you have never used a CAD program before. And perhaps even more importantly: If you cannot draw a layout by hand, you will find it very difficult to the job with software. The software just simplifies some of the tedium of drafting - it does _not_ do the drafting for you. BTW, I've noticed that the people who like these programs design layouts as a hobyy within the hobby.
I took several drafting courses in my younger days -- and I've found that for a small layout (up to about bedroom size), paper and pencil is faster than the computer. I Make a scale outline of the layout space, and put a grid on it. The grid is either 1x1 foot, or in "squares" (footnote). Obstacles, window/door locations etc are all drawn in. Then I make a bunch of photocopies, and skecth the various ideas freehand until I have a couple or three concepts that look good. Those I draw up with compass and ruler. The "final" plan is photocopied again, and benchwork, etc is drawn over the photocopies.
Footnote: A "square" has a side of "min radius + trackspacing + min space to edge of layout." You can fit a quarter circle of double track in it. A layout space subdivided into squares allows you to locate essential curves quickly and easily, and shows you just what might fit. John Armstrong invented the method. You should really get his book; it's essential for serious trackplanning.
Oh, and don't forget aisle space. 2ft is aboslute minimum, 3ft is comfortable for a single operator, and 4ft or more is needed where two operates will be stationed.