Start off with a random picture. We'll use this nice Orli one, as it's the random picture I picked. XD
Once you're done messing around with your picture, go to edit ---> copy
Once it's copied, go to the right of edit ---> effects -----> blinds
A window will pop up. This part is up to you. Screw around with the opacity (How light or dark the lines are) and size (how thick they are). For this one, we'll make it 2 and the opacity 100.
Open up the blinds window again, and keep it how your opacity/size was before - the only difference is now you need to click (or declick if you did the last step with it checked) the horizontal option. This will make a grid-like effect.
Go back up to edit, but this time go to paste and then to paste as new layer. Click it. Your normal, ungridded picture should come up.
Make sure the little box between the magnifying glass and colorful box is selected before you continue.
Click on the rope - it's called freehand.
If you clicked on the box like I told you before, there should be a box that looks like this on your PSP screen. Put the feather on 2 and click on antialias.
With that done, go to your picture and drag your cursor so you highlight a chunk of the picture you WANT to have the grid show on. On your keyboard, there should be a button called 'delete'. If not, simply go to edit again and press clear.
It should look like this now. Repeat these steps until you have everything you want gridded worked on.
Now it should look like this - gridded everywhere except the thing you want to not have gridded. Now it's time to have fun with this. I'll show you how to use MY favorite effect to use with this type of graphic making.
Go to layers ---> properties
Under blend mode, click on Hard Light. I, myself, think it makes the picture sort of blend better together. Feel free to check out the other modes or even keep it as is. Up to you. ^^
If you want to merge the layers together, simply go to Layers ---> Merge ----> Merge all
Now it's just one layer. Do whatever you want with the picture, now. ^^