You can download splatter brush packs at deviantart.
To add them to photoshop, extract the file (if its zipped, if not just move it to this location..) to Hardrive > Program Files > Adobe > Adobe CS3 (or w/e PS your using) > Presets > Brushes.
Now you can load those brushes in adobe. Hope that helps.
If not, another way to attain a splatter efect, is grab a soft brush around 65-100px, and brush once or twice. Now grab your eraser, go into the brush settings and mess about with the dynamics, scattering(quite high, around 400%) etc . Then erase away on the brush layer with 65% opacity and around 40% flow.