I ditto nuknitter. Leave a little white space and the dye will bleed there instead of into each other so much.
You could try to paint it slower. Add one color at a time, let it travel and bleed into the yarn then go back and add the other colors? Not sure if that would work.
Yet another idea:
Resist dying. Take strips of plastic bag (like a thick garbage bag) tie around sections of the yarn. Knitty Gritty did something similar.
I think however, bleeding is gonna happen and I personally love it. It makes a wonderful transition between the colors. I try to pick two colors than when combined make a totally different color. Like a blue section running into a yellow section will make a green bleed section. Or I try to do a gradient effect. Yellow bleeding into orange making a subtle orange between the two.
In any event, practice will make for the results you're looking for. Try joining the dye list groups on yahoo maybe?
Best of luck!