In reply to Chris Ridgers: I was a Paragliding Instructor about 15 years ago (in Snowdonia). I did see quite a few people buying a second hand gliders back then and either teaching themselves or being taught by their paragliding mates. I know of a few locals who taught themselves and went on to be very talented and well known in the world of paragliding (though it has to be said they were climbers who were climbing E6's and E7's at the time so were obviously capable and talented (fearless) individuals).
Most of the others who taught themselves ended up crashing and having pretty bad accidents.
In my time as a paraglider pilot I did witness some horrendous crashes so on balance I would probably recommend completing a course.
Another bit of advice if you can afford it, is to do a course abroad as the weather in the UK is often rubbish. Students would sometimes take well over a year to complete a week long course trying to get flyable weather to coincide with days off work.
And a final word of warning, I was climbing quite well and hadn't really reached my full climbing potential when I discovered and got hooked on Paragliding. I didn't climb for nearly 15 years as Climbing felt rubbish in comparison to flying. Truth is most of the time your waiting around for perfect flying conditions which are quite rare in the UK unless you don't have a job and live in the right area.