Is there a big difference between ukulele and guitar?

The most common tuning for a ukulele is: G C E A

Put a capo on the 5th fret of the guitar and just use the first 4 strings and they will be tuned to G C E A. You can them "simulate" playing a ukulele somewhat using your father's guitar.

It's quite obvious that there are huge difference between guitar and ukulele (size, number of strings, but the biggest is the tuning). The capo trick addresses that issue.

The chords are different. I personally played guitar for 2 years before I got a uke, but it would probably only take a few months. I didn't want a uke until two years after starting guitar. I don't think you could learn ukulele on guitar, though. Maybe buy a cheap uke? I got a fairly good quality, nice looking wood one for £30.

There isn't a really big difference between a ukulele and a guitar. The difference is that the ukulele has got four nylon strings and a guitar has got six strings. So you can practice on your dad's guitar for the time being :) It would be better if your dad has a classical guitar, but it wouldn't matter if it is a acoustic guitar.

They are tuned differently and the chords are not the same, but learning to play open chords on guitars will build the dexterity needed to play chords on a uke. Christmas is not far off so surely you can ask for a uke or get enough xmas money to buy one. For the next 6 weeks you could start practicing some basic open chords on the guitar. I think you'll find once you start playing the uke that you'll want to learn guitar as well.

Yes, guitars have 6 strings and ukuleles only have 4. Guitars and also (obviously) much larger, and the fret boards are wider. The notes are not in the same places either. But you can just mess around on the guitar to get used to picking and playing notes etc.

You can practice the feeling of playing notes on strings, but all the chords are different on guitars and ukuleles and the fret boards and strings are set up differently. So you wont be able to learn a song on 1 instrument, then immediately play it on the other.

Ukuleles are awful. People of a certain age will remember this http://www.youtube.com/watch?v=HeNd0gKH480 In theory a guitar could be tuned to the same scale albeit an octave lower but please don't.

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To play a ukelele, your wrist must be limp.

A ukilali is a lot smaller and has less strings.