It is certainly possible to paint with a texture. These instructions are for CS2 but I know they work in earlier versions.

1. Open the file of the texture you wish to use.
2. Edit>Define Pattern
3. Open Pattern Stamp Tool (under Clone Stamp Tool)
4. Choose your pattern in the pattern choosing tool on the toolbar. The pattern you defined in Step 3 will be the last one in the list.
5. Choose whether you want the pattern Aligned or not
6. Choose a brush and start painting.

HTH,
Barb
BDT Studio