Here is the tutorial ...

sorry ... i kinda mess up the pic when i drew the arrow and stuff hehe ... if i confuse you or u get stuck just let me know ... and i used photoshop 7
NOTE:
step 3: you can change the gradient color to whatever color you like ... just double click on the gradient and select color...
step 4: there are total of 6 colors ... to drag the line ... just hold down your left mouse and drag a line whichever direction you like ... i usually drag it diagonally ... it doesn't matter if you drag outside of the pic

the longer you drag ... the less number of color will appear on the pic ... i don't know how to explain this ... just try you'll see ... this is something i learn along the way

step 7: to duplicate layer just right click on the background layer and choose duplicate ... you can also adjust the opacity and fill to your liking after you change the layer mode to screen .... about the gaussian effect ... the more you do the more blurry it gets
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Result ...
original pic

pic after apply the gradient

I don't know if u can tell the different between these two mode ....
pic with gradient ... and layer mode:
color
pic with gradient ... and layer mode:
hue
--- that's all!