Can I set-up tailgating slimline dish if I have an 18" round standard definition at my home?

What Slimline dish do you have?  3LNB or 5LNB?  And you're sure it's not the Single Wire Multiswitch version?  The SWM version has only one coax output and requires a Power Inserter, while the non-SWM version has four coax outputs and requires no power supply.  

The R16 SD DVR is not HD capable, so if you have the 3LNB Slimline, configure it for "01: Round (18")".  If you have a 5LNB Slimline, configure it for "02: 3-LNB (18"x20")".  But it would be easier to just use another round 18" dish.  There's no benefit using a SlimLine dish with an SD DVR. 

Thanks for the reply Iitzdog.

The dish is a 3LNB with the four coax outputs.  Do I have to repeat satellite setup if the receiver is arleady set for an 18" round?  If not, once I get it pointed at the satellitte, should I get a signal?

If it's already configured for the 18" round dish then it should work just fine when connected to the Slimline 3LNB dish.  Just aim the dish in the same direction as your 18" dish.  You can get the aiming coordinates from http://www.dishpointer.com

Thanks again.  Do I need to know the specific satellite I am aiming at to use Dishpointer?  Also, am I correct to assume that I still set the slimline dish with the noted tilt and skew settings?

You're aiming for the 101ºW satellite.  Since you don't care about the HD satellites, don't worry about tilt/skew.  Just aim for 101º and peak its signal using the Receiver's signal meter.