This forum is intended to specifically support the Photoshop Getting Started experience, and in the future you'll likely get a faster response in the Photoshop forum. That said, here's what you want to do:
- Open Photoshop
- Select File, New
- Enter the size you want, you may need to change the size drop down to pixels
- Clock OK to create the blank canvas
- Select File, Place, this will let you select the image to insert
I'll just add that if you want to create a web page slideshow, then you probably want to use Photoshop to edit or resize the images, and then Dreamweaver to actually build the web pager slideshow.
--- Ben