Lat time I went about 10 years ago I went thru it in a Motor Home. Would recomend camping, that way you can really get the vibe of the Park and up close with the WILD animals
If you have 2 days don't limit yourself to the city of Deadwood. There are tons of things to do in the Black Hills. It is a beautiful area filled with gentle rolling hills with lots of pine trees. You can smell the pine in the air.
If you like snakes try Reptile Gardens near Rapid City. They also have gold mine tours near Deadwood and its sister city Lead (pronounced 'leed', not 'led'). I'll try to find a link for things to do in the area.
Here's a link to a web page that lists Black Hills area attractions. A drive through Spearfish Canyon is nice, especially in the fall when the leaves are turning color.
Quat, thanks for the info, nice links. Yes, we plan on doing more in deadwood than gambling. we are looking for some hiking, and the sites you supplied are very helpful.