Okay, what you are looking at is the result of TWO WHOLE days of hard work, after the first day my hand was aching so much that i can't hold the pen or even the mouse anymore and i had to make a break ;p
The second day i worked on final retouching, working on the mask functions, adding the background and making variations.
I learned a lot by making this one, and when i think about it, it wasn't two days of hard work, it was two days of pure pleasure!

There is so much things to say about it that i'll keep the comments for the tutorial part, for now you can enjoy below two variations:

I made the mask for each parts of the bikini, then i applyied a "express texture effect" with a right scaled silk texture. the masks aren't perfect ( lasso selection ) but it's okay. I applyied a blob effect on the background without retouching again itsuki's shadow on it.
The background is from a game called stars supernova wich will be out in mid-2000.

Using many masks i can thus select easily the part of the swinsuit i wanted to fill with a grandient effect ( plus another texture effect ). Same for the background ( plus an effect i can't remeber the name but wich generated the white dots ). Made darker outline shadow for itsuki this time. I still use 2 layers plus the canvas but i had to "lasso select" the whole itsuki body shape , not that easy you know! the point2point selection is badly missing in painter 6 imo.