Photoshop gradient fill

[Daz]

Ok it might be kinda hard to explain this one but here goes. I want to achieve a fill effect in a vertical rectangle going top top bottom where it fades at the bottom. Now at the top, about 2/3 of th fill is solid and as you work up from the bottom you have thin white lines which increase in width until they reach say 20px high. The closest I can get to this is with the transparent stripes and reflected gradient but the white lines and coloured lines are equal spacing. I want them to be less spaced out as I reach the end. Does that make sense?!

[Daz]

Here's the kinda thing I mean on the left menu only I want the white lines to go from thick to thin.

http://www.acquiweb.com/abacus/pics/abacus.gif

[anode]

Just do it manually with the rectangular marquee and your backspace key.