Sure you can use PSP8
I use PSPX to add my watermarks, but it should be the same in 8 too. What I do is to add either a new layer, add my text and then turn down the transparency before merging the two layers.
Or you could add text as a selection and then add a drop shadow with offset, set to zero (0) in both directions.
If you get to do a lot of pictures where you need a watermark you could make a brush out of it and just stamp the image with the brush before saving. I don't remember if 8 had preset shapes, but you could also make a watermark and save it as a preset shape.