This topic has been up a few times before I think, have you tried doing a search through old posts in the tech section? There is a 'Search' link near the top of the page just below the banner that a lot of people probably aren't aware of. :thumb
I haven't done it myself, and not paid much attention to the process, as my '75 kombi is already IRS (double jointed) and with my notch it will be easier to unbolt the whole rear suspension assembly and bolt an IRS assembly in its place. Unfortunately I don't think that can be done on a Beetle.
I believe that the conversion involves drilling suspension plates, welding on suspension brackets to the torsion bar housing, installing the inner arms, IRS hub assembly, IRS gearbox (or was it just the side covers and flanges?), CV's and driveshaft, then aligning the rear wheels.
Try the search, you will probably find better answers. 🙂
Kruizin Kol