.38 S&W is the same as .38 Colt New Police.
If the revolver says "Police Positive Special" then it is chambered for .38 Special and will use that. This is probably not the case though.
If it is a regular Police Positive, it was made in 1909, if it is a Special, it was made in 1910.
Without seeing the gun, it's hard to say if you got a good deal or not. In good shape, they can go for ~$250, and like new versions may command over $400, but it sounds like yours is cosmetically a little beaten up, so you probably got an average deal.
As for whether it's a decent house gun, that depends largely on how accurate you are when you shoot it. It should be reliable, but it's not a terribly powerful loading. Still, it will do its job if you do yours.