You can easily transform an existing acoustic guitar into a temporary lap slide guitar with an extension nut.  You will also need a steel designed for squareneck playing (Scheerhorn, Tipton, LapDawg), a good quality thumbpick (Golden Gate, Zookies) and 2 fingerpicks. You can find these items at Elderly or First Quality Music

 I already play guitar, can I apply my guitar based skills to dobro? Is the technique the same?

While it goes without saying that the left hand technique is quite different, the right hand technique to playing dobro/Weissenborn guitar is based on basic fingerpicking skills, but with some twists:

Rolls are highly syncopated chord structures played one note at a time, in a specific sequence, (sometimes referred to as an arpeggio) often at breakneck tempo. The right hand technique to rolls, especially in a bluegrass context, has more in common with the banjo than the guitar (listen to Fireball - in tablature section - for an example of G roll based tune). In other cases a roll pattern can be very similar to a fingerstyle guitar arrangement - it all depends on the tune and the player. For bluegrass dobro (which is normally G tuning-G-B-D-G-B-D) the ability to play a G roll is probably the single most important roll!!

Chop is similar to mandolin chop and functions in the same way: usually plays the offbeat (one and two and three, etc. (example: I use a chop to play rhythm when the mandolin plays the melody in the Big Mon video clip-tablature section)

In addition to the above -the real twist in right hand technique is in playing the ornaments and embellishments native to the dobro, namely, the hammer-on's, pull-off's, slides and slurs used to express melodies and licks. In basic terms, the thumb is the lead, while the 1st and 2nd fingers fill out the rest of the notes. The thumb almost always plays pull-offs, and plays on any string, including the 1st string! I have heard it said that 80% of a players tone on the dobro comes from their right hand. The right hand technique make a huge difference!

 What should I focus on when learning to play dobro/Weissenborn? Is it better to practice scales and  licks or should I play songs?

There is no magic formula or technique that works for everyone, but here are a few guidelines that I have found to be helpful:

• Learning to play an instrument is an evolutionary process. It takes years of practice for most of us just to play a simple song extremely well
• There is no single "correct" way to play dobro or Weissenborn guitar - there are only starting points
• Tablature without right hand fingerings can lead to poor technique/bad habits for beginners
• Pay strict attention to the right hand fingerings when learning new tunes. It may even seem counter-intuitive but it will save you a lot of time in the long run.
• Its more fun to practice tunes than scales, but scales are like roadmaps that can help save time, especially when you are a beginner
• You can cover a lot of ground if you have a grasp of just three basic scales-major, minor and pentatonic scales
• A knowledge of basic music theory won't make you play like Jerry Douglas, but it will make you a "quick study" when it comes to deciphering chord progressions and/or improvising solos over tunes that you have never heard before
• It is helpful, dare I say - liberating - to develop an understanding of chord progressions in non-key-specific-terms. Have you ever jammed with someone who tried to teach you a new tune..."this tune starts out with a G, then D, back to G," etc, etc, etc? Thinking in non-key-specific terms forces you to view chord progressions in terms of relationships between chords--same example..."the kickoff is a quick I-V-I, watch out for the II chord in the chorus"...
• For anyone interested in understanding music theory I highly recommend you pick up a copy of Edly's Music Theory for Practical People.  Check out his website... http://www.edly.com
• It is critical to practice with some kind of time keeper, metronome or drum machine
• Tablature is a great time saver, but nothing can replace the value of learning tunes by ear.
• If you are new to the instrument, start by learning children's tunes or simple folk songs in the key of G. Strum an open G chord and sing the melody to a song (start with something you can sing by heart - Home on the range, Over the rainbow, a kids song, etc)-now find the notes! Gradually add chords and embellishments like slides, pull-off's, etc.
• Once you can play even moderately well, it is absolutely critical to get out of the house and play with other musicians. Join a band, play at church, go to open-mic nights - do whatever it takes - force yourself if necessary - to put yourself in situations where you learn to play with others.