DeskPaint! It's a DA and I know it came with a book called "Cool Mac Clip Art Plus" by Tony Reveneaux. The book was published by Hayden, the same guys who put out the games book I talked about not long ago here. (It also has some clip art on the disk). It's monochrome although I think you could buy a colour version as well. I believe it is commercial software, so you're on your own finding a copy of it. It does MacPaint, PICT, and TIFF. (There's also a DeskDraw, which is like pocket MacDraw, but I don't have it and haven't tried it...just read about it).
If the files are MacPaint and you have a copy of WetPaint, use ArtRoundUp. It's read-only but is very good. It came with any copy of WetPaint. Use Version 2.7 for best results with System 7 (though 2.5 also works). Dubl-Click sold this until they went out as a seperate program.
You can also find a copy of Mac Secrets, which contains Color It. It's bundled like DeskPaint is. It can read a lot of formats and you'll want the older version for a Classic (get the 2nd edition of Secrets).
Don't forget that if you're using something other than what one of these programs can read you can use the shareware utility GraphicConverter for OS 9 or X to convert them to a different format.